Patterns of Inheritance Chapter 9 Patterns of Inheritance © 2016 Pearson Education, Inc.

Figure 9.0-1 Why Genetics Matters Figure 9.0-1 Why genetics matters

Figure 9.0-1a Figure 9.0-1a Why genetics matters (part 1: sex determination)

Figure 9.0-1b Figure 9.0-1b Why genetics matters (part 2: role of environment)

Figure 9.0-1c Figure 9.0-1c Why genetics matters (part 3: genetic disorders)

Biology and Society: Our Longest-Running Genetic Experiment People have selected and mated dogs with preferred traits for more than 15,000 years. Over thousands of years, such genetic tinkering has led to the incredible variety of body types and behaviors in dogs today. The biological principles underlying genetics have only recently been understood. © 2016 Pearson Education, Inc. 6

Chapter Thread: Dog Breeding Figure 9.0-2 Chapter Thread: Dog Breeding Figure 9.0-2 Dog breeding: breeding a best friend

Genetics and Heredity Heredity is the transmission of traits from one generation to the next. Genetics is the scientific study of heredity. Gregor Mendel worked in the 1860s and argued that parents pass on to their offspring discrete genes (which he termed “heritable factors”), genes are responsible for inherited traits, and genes retain their individual identities generation after generation, no matter how they are mixed up or temporarily masked. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 8

Figure 9.1 Figure 9.1 Gregor Mendel

In an Abbey Garden Mendel probably chose to study garden peas because they were easy to grow and came in many readily distinguishable varieties. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 10

In an Abbey Garden A character is a heritable feature that varies among individuals. A trait is a variant of a character. Each of the characters Mendel studied occurred in two distinct traits. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 11

In an Abbey Garden Perhaps the most important advantage of pea plants as an experimental model was that Mendel could strictly control their reproduction. The petals of a pea flower almost completely enclose the egg-producing organ (the carpel) and the sperm-producing organs (the stamens). Consequently, pea plants usually self-fertilize because sperm-carrying pollen grains released from the stamens land on the tip of the egg-containing carpel of the same flower. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 12

Petal Stamen (makes sperm- producing pollen) Carpel (produces eggs) Figure 9.2 Petal Stamen (makes sperm- producing pollen) Carpel (produces eggs) Figure 9.2 The structure of a pea flower

In an Abbey Garden When Mendel wanted to fertilize one plant with pollen from a different plant, he pollinated the plants by hand and was always sure of the parentage of his new plants. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 14

Transferred pollen from stamens of white flower Figure 9.3-s1 Removed stamens from purple flower. Stamens Parents (P) Transferred pollen from stamens of white flower to carpel of purple flower. Carpel Figure 9.3-s1 Mendel’s technique for cross-fertilizing pea plants (step 1)

Transferred pollen from stamens of white flower Figure 9.3-s2 Removed stamens from purple flower. Stamens Parents (P) Transferred pollen from stamens of white flower to carpel of purple flower. Carpel Pollinated carpel matured into pod. Figure 9.3-s2 Mendel’s technique for cross-fertilizing pea plants (step 2)

Transferred pollen from stamens of white flower Figure 9.3-s3 Removed stamens from purple flower. Stamens Parents (P) Transferred pollen from stamens of white flower to carpel of purple flower. Carpel Pollinated carpel matured into pod. Planted seeds from pod. Offspring (F1) Figure 9.3-s3 Mendel’s technique for cross-fertilizing pea plants (step 3)

In an Abbey Garden Mendel created purebred varieties of plants and crossed two different purebred varieties. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 18

In an Abbey Garden Hybrids are the offspring of two different purebred varieties. The cross-fertilization itself is referred to as a genetic cross. The parental plants are the P generation. Their hybrid offspring are the F1 generation. A cross of the F1 plants forms the F2 generation. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 19

Mendel’s Law of Segregation Mendel performed many experiments in which he tracked the inheritance of characters, such as flower color, that occur as two alternative traits. The results led him to formulate several hypotheses about inheritance. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

Dominant Recessive Dominant Recessive Flower color Pod shape Inflated Figure 9.4 Dominant Recessive Dominant Recessive Flower color Pod shape Inflated Constricted Purple White Pod color Flower position Green Yellow Stem length Axial Terminal Seed color Yellow Green Tall Dwarf Seed shape Round Wrinkled Figure 9.4 The seven characters of pea plants studied by Mendel

Figure 9.4-1 Figure 9.4-1 The seven characters of pea plants studied by Mendel (part 1: pea plant photo)

Monohybrid Crosses Mendel performed a monohybrid cross between purebred parent plants that differ in only one character and found that the F1 plants all had purple flowers. Was the factor responsible for inheritance of white flowers now lost as a result of the cross? By mating the F1 plants with each other, Mendel found the answer to this question to be no. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 23

Purple flowers White flowers Figure 9.5-s1 P Generation (purebred parents) Purple flowers White flowers Figure 9.5-s1 Mendel’s cross tracking one character (flower color) (step 1)

P Generation (purebred parents) Purple White flowers flowers Figure 9.5-s2 P Generation (purebred parents) Purple flowers White flowers F1 Generation All plants have purple flowers Figure 9.5-s2 Mendel’s cross tracking one character (flower color) (step 2)

P Generation (purebred parents) Purple White flowers flowers Figure 9.5-s3 P Generation (purebred parents) Purple flowers White flowers F1 Generation All plants have purple flowers Fertilization among F1 plants (F1 × F1) F2 Generation 3 4 1 4 of plants have purple flowers of plants have white flowers Figure 9.5-s3 Mendel’s cross tracking one character (flower color) (step 3)

Figure 9.5-1 Figure 9.5-1 Mendel’s cross tracking one character (flower color) (part 1: portrait of Mendel)

Monohybrid Crosses Mendel figured out that the gene for white flowers did not disappear in the F1 plants but was somehow hidden or masked when the purple- flower factor was present. He also deduced that the F1 plants must have carried two factors for the flower-color character, one for purple and one for white. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 28

Monohybrid Crosses From these results and others, Mendel developed four hypotheses: There are alternative versions of genes that account for variations in inherited characters. The alternative versions of genes are called alleles. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 29

Monohybrid Crosses For each inherited character, an organism inherits two alleles, one from each parent. An organism that has two identical alleles for a gene is said to be homozygous for that gene. An organism that has two different alleles for a gene is said to be heterozygous for that gene. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 30

Monohybrid Crosses If the two alleles of an inherited pair differ, then one determines the organism’s appearance and is called the dominant allele, and the other has no noticeable effect on the organism’s appearance and is called the recessive allele. Geneticists use uppercase italic letters (such as P) to represent dominant alleles and lowercase italic letters (such as p) to represent recessive alleles. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 31

Monohybrid Crosses A sperm or egg carries only one allele for each inherited character because the two alleles for a character segregate (separate) from each other during the production of gametes. This statement is called the law of segregation. When sperm and egg unite at fertilization, each contributes its alleles, restoring the paired condition in the offspring. Figure 9.6 illustrates Mendel’s law of segregation, which explains the inheritance pattern shown in Figure 9.5. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 32

Genetic makeup (alleles) Figure 9.6 P Generation Genetic makeup (alleles) Purple flowers White flowers Alleles carried by parents PP pp Gametes All P All p F1 Generation (hybrids) Purple flowers Alleles segregate Gametes All Pp 1 2 1 2 P p F2 Generation (hybrids) Sperm from F1 plant P p P Eggs from F1 plant PP Pp p Pp pp Phenotypic ratio 3 purple:1 white Genotypic ratio 1 PP:2 Pp:1 pp Figure 9.6 The law of segregation

Genetic makeup (alleles) Figure 9.6-1 P Generation Genetic makeup (alleles) Purple flowers White flowers Alleles carried by parents PP pp Gametes All P All p F1 Generation (hybrids) Purple flowers Alleles segregate Gametes All Pp 1 2 1 2 p P Figure 9.6-1 The law of segregation (part 1: P generation and F1 generation)

F1 Generation (hybrids) Purple flowers Alleles segregate Gametes All Figure 9.6-2 F1 Generation (hybrids) Purple flowers Alleles segregate Gametes All Pp 1 2 1 2 P p F2 Generation (hybrids) Sperm from F1 plant P p P Eggs from F1 plant PP Pp p Pp pp Phenotypic ratio 3 purple:1 white Genotypic ratio 1 PP:2 Pp:1 pp Figure 9.6-2 The law of segregation (part 2: F2 generation)

Monohybrid Crosses A Punnett square highlights the four possible combinations of gametes and the resulting four possible offspring in the F2 generation. Each square represents an equally probable product of fertilization. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 36

Monohybrid Crosses Geneticists distinguish between an organism’s physical appearance, its phenotype, and genetic makeup, its genotype. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 37

Monohybrid Crosses Mendel found that each of the seven characters he studied had the same inheritance pattern: A parental trait disappeared in the F1 generation, only to reappear in one-fourth of the F2 offspring. The underlying mechanism is explained by Mendel’s law of segregation: Pairs of alleles segregate during gamete formation; the fusion of gametes at fertilization creates allele pairs again. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 38

Genetic Alleles and Homologous Chromosomes The diagram in Figure 9.7 shows a pair of homologous chromosomes—chromosomes that carry alleles of the same genes. A gene locus is a specific location of a gene along a chromosome. Alleles (alternative versions) of a gene reside at the same locus on homologous chromosomes. However, the two chromosomes may bear either identical alleles or different ones at any one locus. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 39

Homologous chromosomes Gene loci Dominant allele P a B P a b Recessive Figure 9.7 Homologous chromosomes Gene loci Dominant allele P a B P a b Recessive allele Genotype: PP aa Bb Homozygous for the dominant allele Homozygous for the recessive allele Heterozygous with one dominant and one recessive allele Figure 9.7 The relationship between alleles and homologous chromosomes

Mendel’s Law of Independent Assortment A dihybrid cross is the mating of parental varieties differing in two characters. What would result from a dihybrid cross? © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 41

Mendel’s Law of Independent Assortment If the genes for the two characters were inherited together, then the F1 hybrids would produce only the same two kinds of gametes that they received from their parents, and the F2 generation would show a 3:1 phenotypic ratio. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 42

Mendel’s Law of Independent Assortment If, however, the two seed characters sorted independently, then the F1 generation would produce four gamete genotypes (RY, rY, Ry, and ry) in equal quantities, and the F2 generation would have nine different genotypes producing four different phenotypes in a ratio of 9:3:3:1. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 43

Independent assortment Figure 9.8 (a) Hypothesis: Dependent assortment (b) Hypothesis: Independent assortment P Generation RRYY rryy RRYY rryy Gametes ry Gametes RY RY ry F1 Generation RrYy RrYy F2 Generation Sperm 1 4 RY 1 4 rY 1 4 Ry 1 4 ry Sperm 1 2 RY 1 2 ry 1 4 RY RRYY RrYY RRYy RrYy 1 2 RY 1 4 rY Eggs 9 16 Yellow round RrYY RrYy rrYy Eggs rrYY 1 2 ry 1 4 Ry 3 16 Green round RRYy RrYy RRyy Rryy 1 4 Yellow wrinkled ry 3 16 RrYy rrYy Rryy rryy Predicted results (not actually seen) Actual results (support hypothesis) Green wrinkled 1 16 Figure 9.8 Testing alternative hypotheses for gene assortment in a dihybrid cross

Independent assortment Figure 9.8-1 (a) Hypothesis: Dependent assortment (b) Hypothesis: Independent assortment P Generation RRYY rryy RRYY rryy Gametes RY ry Gametes RY ry F1 Generation RrYy RrYy Figure 9.8-1 Testing alternative hypotheses for gene assortment in a dihybrid cross (part 1: hypothesis)

Predicted results (not actually seen) Figure 9.8-2 F2 Generation Sperm 1 2 1 2 RY ry 1 2 RY Eggs 1 2 ry Predicted results (not actually seen) Figure 9.8-2 Testing alternative hypotheses for gene assortment in a dihybrid cross (part 2: predicted results)

Actual results (support hypothesis) Figure 9.8-3 Sperm F2 Generation 1 4 1 4 1 4 1 4 RY rY Ry ry 1 4 RY RRYY RrYY RRYy RrYy 1 4 rY Yellow round 9 16 RrYY rrYY RrYy rrYy Eggs 1 4 Ry Green round 3 16 RRYy RrYy RRyy Rryy 1 4 Yellow wrinkled 3 16 ry RrYy rrYy Rryy rryy Actual results (support hypothesis) Green wrinkled 1 16 Figure 9.8-3 Testing alternative hypotheses for gene assortment in a dihybrid cross (part 3: actual results)

Figure 9.8-4 Figure 9.8-4 Testing alternative hypotheses for gene assortment in a dihybrid cross (part 4: peas photo)

Mendel’s Law of Independent Assortment Mendel’s dihybrid cross supported the hypothesis that each pair of alleles segregates independently of the other pairs during gamete formation. Thus, the inheritance of one character has no effect on the inheritance of another. This is called Mendel’s law of independent assortment. Independent assortment is seen in the inheritance of two characters in Labrador retrievers. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 49

Mating of double heterozygotes (black coat, normal vision) Figure 9.9 Blind dog Blind dog Phenotypes Black coat, normal vision Black coat, blind (PRA) Chocolate coat, normal vision Chocolate coat, blind (PRA) Genotypes B_N_ B_nn bbN_ bbnn (a) Possible phenotypes of Labrador retrievers Mating of double heterozygotes (black coat, normal vision) BbNn BbNn Blind Blind Phenotypic ratio of offspring 9 black coat, normal vision 3 black coat, blind (PRA) 3 chocolate coat, normal vision 1 chocolate coat, blind (PRA) (b) A Labrador dihybrid cross Figure 9.9 Independent assortment of genes in Labrador retrievers

(a) Possible phenotypes and genotypes of Labrador retrievers Figure 9.9-1 (a) Possible phenotypes and genotypes of Labrador retrievers Blind dog Blind dog Black coat, normal vision B_N_ Black coat, blind (PRA) B_nn Chocolate coat, normal vision bbN_ Chocolate coat, blind (PRA) bbnn Figure 9.9-1 Independent assortment of genes in Labrador retrievers (part 1: possible phenotypes and genotypes)

Mating of double heterozygotes Figure 9.9-2 Mating of double heterozygotes (BbNn × BbNn) Blind 9 black coat, normal vision 3 black coat, blind (PRA) Blind 3 chocolate coat, normal vision 1 chocolate coat, blind (PRA) Figure 9.9-2 Independent assortment of genes in Labrador retrievers (part 2: Labrador dihybrid cross)

Using a Testcross to Determine an Unknown Genotype A testcross is a mating between an individual of dominant phenotype (but unknown genotype) and a homozygous recessive individual. Figure 9.10 shows the offspring that could result from such a mating. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 53

Two possible genotypes for the black dog: Figure 9.10 Testcross Genotypes B_ bb Two possible genotypes for the black dog: BB or Bb Gametes B B b b Bb b Bb bb Offspring All black 1 black : 1 chocolate Figure 9.10 A Labrador retriever testcross

The Rules of Probability Mendel’s strong background in mathematics helped him understand patterns of inheritance. For instance, he understood that genetic crosses obey the rules of probability—the same rules that apply when tossing coins, rolling dice, or drawing cards. The rule of multiplication states that the probability of a compound event is the product of the separate probabilities of the independent events. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 55

( ) F1 Genotypes Bb female Bb male Formation of eggs Figure 9.11 F1 Genotypes Bb female × Bb male Formation of eggs Formation of sperm F2 Genotypes Male gametes 1 2 1 2 B b B B B b 1 2 B 1 4 1 4 ( 1 2 1 2 ) Female gametes × 1 2 b b b b B 1 4 1 4 Figure 9.11 Segregation of alleles and fertilization as chance events

Family Pedigrees Mendel’s principles apply to the inheritance of many human traits. Figure 9.12 illustrates alternative forms of three human characters that are each thought to be determined by simple dominant-recessive inheritance of one gene. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 57

DOMINANT TRAITS Freckles Widow’s peak Free earlobe RECESSIVE TRAITS Figure 9.12 DOMINANT TRAITS Freckles Widow’s peak Free earlobe RECESSIVE TRAITS No freckles Straight hairline Attached earlobe Figure 9.12 Examples of inherited human traits thought to be controlled by a single gene

Freckles No freckles Figure 9.12-1 Figure 9.12-1 Examples of inherited human traits thought to be controlled by a single gene (part 1: freckles)

Widow’s peak Straight hairline Figure 9.12-2 Figure 9.12-2 Examples of inherited human traits thought to be controlled by a single gene (part 2: widow’s peak)

Free earlobe Attached earlobe Figure 9.12-3 Figure 9.12-3 Examples of inherited human traits thought to be controlled by a single gene (part 3: earlobes)

Family Pedigrees A trait that is dominant does not imply that it is either normal or more common than a recessive phenotype. Wild-type traits (those seen most often in nature) are not necessarily specified by dominant alleles. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 62

Family Pedigrees How can human genetics be studied? Geneticists analyze the results of matings that have already occurred and assemble this information into a family tree, called a pedigree. Figure 9.13 shows a pedigree tracing the incidence of free versus attached earlobes. Mendel’s laws enable us to deduce the genotypes for most of the people in the pedigree. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 63

First generation (grandparents) Aaron Ff Betty Ff Cletus ff Debbie Ff Figure 9.13-1 First generation (grandparents) Aaron Ff Betty Ff Cletus ff Debbie Ff Second generation (parents, aunts, and uncles) Evelyn FF or Ff Fred ff Gabe ff Hal Ff Ina Ff Julia ff Third generation (brother and sister) Kevin ff Lisa FF or Ff Female Male Female Male Attached Free Figure 9.13-1 A family pedigree showing inheritance of free versus attached earlobes (part 1: pedigree)

Figure 9.13-2 Figure 9.13-2 A family pedigree showing inheritance of free versus attached earlobes (part 2: family)

Figure 9.13-3 Figure 9.13-3 A family pedigree showing inheritance of free versus attached earlobes (part 3: attached)

Figure 9.13-4 Figure 9.13-4 A family pedigree showing inheritance of free versus attached earlobes (part 4: free)

Human Disorders Controlled by a Single Gene Some human genetic disorders are known to be inherited as dominant or recessive traits controlled by a single gene, all located on autosomes, chromosomes other than the sex chromosomes X and Y. These disorders are listed in Table 9.1. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 68

Table 9.1 Table 9.1 Some autosomal disorders in people

Recessive Disorders Most human genetic disorders are recessive. Individuals who have the recessive allele but appear normal are carriers of the disorder. Using Mendel’s laws, we can predict the fraction of affected offspring that is likely to result from a marriage between two carriers. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 70

Parents Hearing Dd Hearing Dd Offspring D d Sperm Dd Hearing (carrier) Figure 9.14 Parents Hearing Dd Hearing Dd Offspring D d Sperm Dd Hearing (carrier) DD Hearing D Eggs Dd Hearing (carrier) dd Deaf d Figure 9.14 Predicted offspring when both parents are carriers for a recessive disorder

Recessive Disorders Cystic fibrosis is the most common lethal genetic disease in the United States and caused by a recessive allele carried by about 1 in 31 Americans. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 72

Dominant Disorders A number of human disorders are caused by dominant alleles. Achondroplasia is a form of dwarfism. The homozygous dominant genotype (AA) causes death of the embryo. Therefore, only heterozygotes (Aa), individuals with a single copy of the defective allele, have this disorder. This also means that a person with achondroplasia has a 50% chance of passing the condition on to any children. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 73

Parents Normal (no achondroplasia) dd Dwarf (achondroplasia) Dd d d Figure 9.15 Parents Normal (no achondroplasia) dd Dwarf (achondroplasia) Dd d d Sperm Dd Dwarf Dd Dwarf D Eggs dd Normal dd Normal d Figure 9.15 A Punnett square illustrating a family with and without achondroplasia

Dominant Disorders Dominant alleles that cause lethal disorders are much less common than lethal recessive alleles. One example is the allele that causes Huntington’s disease, a degeneration of the nervous system that usually does not begin until middle age. Once the deterioration of the nervous system begins, it is irreversible and inevitably fatal. Because the allele for Huntington’s disease is dominant, any child born to a parent with the allele has a 50% chance of inheriting the allele and the disorder. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 75

The Process of Science: What Is the Genetic Basis of Coat Variation in Dogs? Observation: Dogs come in a wide variety of physical types. Question: What is the genetic basis for canine coats? Hypothesis: A comparison of genes of a wide variety of dogs with different coats would identify the genes responsible. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 76

Figure 9.16 Figure 9.16 Smooth versus wired fox terrier

The Process of Science: What Is the Genetic Basis of Coat Variation in Dogs? Prediction: Mutations in just a few genes account for the coat appearance. Experiment: Researchers compared DNA sequences of 622 dogs from dozens of breeds. Results: Three genes in different combinations produced seven different coat appearances, from very short hair to full, thick, wired hair. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 78

Genetic Testing Today many tests can detect the presence of disease-causing alleles. Most genetic tests are performed during pregnancy if the prospective parents are aware that they have an increased risk of having a baby with a genetic disease. In amniocentesis, a physician uses a needle to extract about 2 teaspoons of the fluid that bathes the developing fetus. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 79

Genetic Testing In chorionic villus sampling, a physician inserts a narrow, flexible tube through the mother’s vagina and into her uterus, removing some placental tissue. Newer genetic screening procedures involve isolating tiny amounts of fetal cells or DNA released into the mother’s bloodstream. These newer technologies are gradually replacing more invasive screening methods because they are more accurate and can be performed earlier than other tests. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 80

Figure 9.17 Figure 9.17 Amniocentesis

Genetic Testing Once cells are obtained, they can be screened for genetic diseases. Patients seeking genetic testing should receive counseling both before and after to explain the test and to help them cope with the results. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture. 2. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling reflects expected ratios. 3. The authors note that Mendel’s work was published in 1866, seven years after Darwin published On the Origin of Species. Consider challenging your students to consider whether Mendel’s findings were supportive of Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet Mendel’s selection of pea plant traits typically showed complete dominance. Mendel’s pea traits did not show the possibility for such gradual inheritance. Teaching Tips 1. Medical technology raises many ethical issues. Consider asking your students this practical question: How much routine fetal testing do we want our insurance companies to cover and at what cost for insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay? 2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress. 3. Consider this analogy for dominance of a trait in the heterozygous condition, which may help struggling students. Two people are trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. If this “heterozygous” couple eats at home, the dominant allele “wins.” 4. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP × pp and (b) Pp × pp. 5. Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses. 6. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. Explanation: If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three black and one chocolate or all black. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype. 7. The 2/3 fraction noted in the discussion of carriers of a recessive disorder (and in Figure 9.14) often catches students off guard, as they may be expecting odds of 1/4, 1/2, or 3/4. However, we eliminate the dd (deaf) possibility, as it would not be a carrier. So, the odds are based out of the remaining three genotypes Dd, dD, and DD. 8. Genetic tests are now available to inform a person whether he or she has the Huntington’s allele. The test is especially important to the children of a parent with Huntington’s disease. Consider asking your class (a) what are the odds of developing Huntington’s disease if a parent has this disease (50%) and (b) whether or not they would want this genetic test. The Huntington Disease Society website (www.hdsa.org) offers many additional details. It is a good starting point for those who want to explore this disease in more detail. Active Lecture Tips 1. Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities. 2. As a simple test of comprehension, ask students to work in pairs to explain why lethal alleles are not eliminated from a population. Several possibilities exist: (a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or (b) the lethal allele might be dominant, but is not expressed until after the age of reproduction. 3. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 4. See the activity Interactive Celebrity Parents Genetic Inheritance Game on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 5. See the activity Personal Genomics: Would You Give Your DNA Away? on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 82

Variations on Mendel’s Laws Mendel’s two laws explain inheritance in terms of genes that are passed along from generation to generation according to simple rules of probability. These laws are valid for all sexually reproducing organisms. But Mendel’s laws stop short of explaining some patterns of genetic inheritance. In fact, for most sexually reproducing organisms, cases in which Mendel’s rules can strictly account for the patterns of inheritance are relatively rare. More often, the observed inheritance patterns are more complex. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. As these variations of Mendel’s laws are introduced, students are likely to get confused and become uncertain about the prior definitions. Consider keeping a clear definition of these different patterns of inheritance available for the class to refer to as new patterns are discussed (perhaps as a handout for student reference). 2. As your class size increases, the chances increase that at least one student will have a family member with one of the genetic disorders discussed. Some students may find this embarrassing, but others might have a special interest in learning more about these topics, and may even be willing to share some of their family’s experiences with the class. Teaching Tips 1. Incomplete dominance is analogous to a compromise, or a shade of gray. The key concept is that both “sides” have input. Complete dominance is more analogous to an authoritarian style, overruling others and insisting on things being a certain way. Although these analogies might seem obvious to us, many students new to genetics appreciate them. 2. Another analogy for cholesterol receptors is fishing poles. The more fishing poles you use, the more fish you will likely catch. Heterozygotes for hypercholesterolemia have fewer “fishing poles” for cholesterol. Thus, fewer “fish” are caught and more “fish” remain in the water. 3. Students can think of blood types as analogous to socks on their feet. You can have socks that match, a sock on one foot but not the other, you can wear two socks that do not match, or you can even go barefoot (type O blood)! Developed further, think of amber (A) and blue (B) socks. Type A blood can have an amber sock with either another amber sock or a bare foot (or “zero” sock). Blue socks work the same way. One amber and one blue sock represent the AB blood type. Having no socks, as already noted, represents type O. 4. Consider specifically comparing the principles of codominance (expression of both alleles) and incomplete dominance (expression of one intermediate trait). Students will likely benefit from this direct comparison. 5. The American Sickle Cell Anemia Association’s website (www.ascaa.org) is a good place to get additional details. 6. Polygenic inheritance makes it possible for children to inherit genes to be taller, or shorter, than either parent. Similarly, skin tones can be darker or lighter than either parent. The environment also contributes significantly to the final phenotype for both of these traits. 7. The authors note that polygenic inheritance is the converse of pleiotropy. This is worth noting in lecture as these concepts are discussed. We often remember concepts better when they are contrasted in pairs. 8. As the authors are careful to note, although genetics and the environment both contribute to the final phenotypes, only the genetic factors are inherited. This distinction is important to understanding the limitations of Lamarck’s mechanisms of evolution. If you will address principles of evolution soon after this chapter, this may be an important distinction to reinforce in lecture. References to tattoos, piercing, and circumcision may also help to distinguish between environmental influences and inheritance. Students with tattoos will not produce children born with tattoos! And for thousands of years, fathers who are circumcised have not fathered boys also circumcised! Active Lecture Tips 1. See the activity Who Wants to Be a Millionaire? Inheritance on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 83

Incomplete Dominance in Plants and People In incomplete dominance, F1 hybrids have an appearance between the phenotypes of the two parents. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. As these variations of Mendel’s laws are introduced, students are likely to get confused and become uncertain about the prior definitions. Consider keeping a clear definition of these different patterns of inheritance available for the class to refer to as new patterns are discussed (perhaps as a handout for student reference). 2. As your class size increases, the chances increase that at least one student will have a family member with one of the genetic disorders discussed. Some students may find this embarrassing, but others might have a special interest in learning more about these topics, and may even be willing to share some of their family’s experiences with the class. Teaching Tips 1. Incomplete dominance is analogous to a compromise, or a shade of gray. The key concept is that both “sides” have input. Complete dominance is more analogous to an authoritarian style, overruling others and insisting on things being a certain way. Although these analogies might seem obvious to us, many students new to genetics appreciate them. 2. Another analogy for cholesterol receptors is fishing poles. The more fishing poles you use, the more fish you will likely catch. Heterozygotes for hypercholesterolemia have fewer “fishing poles” for cholesterol. Thus, fewer “fish” are caught and more “fish” remain in the water. 3. Students can think of blood types as analogous to socks on their feet. You can have socks that match, a sock on one foot but not the other, you can wear two socks that do not match, or you can even go barefoot (type O blood)! Developed further, think of amber (A) and blue (B) socks. Type A blood can have an amber sock with either another amber sock or a bare foot (or “zero” sock). Blue socks work the same way. One amber and one blue sock represent the AB blood type. Having no socks, as already noted, represents type O. 4. Consider specifically comparing the principles of codominance (expression of both alleles) and incomplete dominance (expression of one intermediate trait). Students will likely benefit from this direct comparison. 5. The American Sickle Cell Anemia Association’s website (www.ascaa.org) is a good place to get additional details. 6. Polygenic inheritance makes it possible for children to inherit genes to be taller, or shorter, than either parent. Similarly, skin tones can be darker or lighter than either parent. The environment also contributes significantly to the final phenotype for both of these traits. 7. The authors note that polygenic inheritance is the converse of pleiotropy. This is worth noting in lecture as these concepts are discussed. We often remember concepts better when they are contrasted in pairs. 8. As the authors are careful to note, although genetics and the environment both contribute to the final phenotypes, only the genetic factors are inherited. This distinction is important to understanding the limitations of Lamarck’s mechanisms of evolution. If you will address principles of evolution soon after this chapter, this may be an important distinction to reinforce in lecture. References to tattoos, piercing, and circumcision may also help to distinguish between environmental influences and inheritance. Students with tattoos will not produce children born with tattoos! And for thousands of years, fathers who are circumcised have not fathered boys also circumcised! Active Lecture Tips 1. See the activity Who Wants to Be a Millionaire? Inheritance on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 84

P Generation Red White RR rr Gametes R r Figure 9.18-s1 Figure 9.18-s1 Incomplete dominance in snapdragons (step 1)

P Generation Red White RR rr Gametes F1 Generation Pink Rr Gametes R r Figure 9.18-s2 P Generation Red RR White rr Gametes R r F1 Generation Pink Rr Gametes 1 2 1 2 R r Figure 9.18-s2 Incomplete dominance in snapdragons (step 2)

Red RR White rr Pink Rr Sperm Eggs Figure 9.18-s3 P Generation Red RR White rr Gametes R r F1 Generation Pink Rr Gametes 1 2 1 2 R r F2 Generation Sperm 1 2 1 2 R r 1 2 R Eggs RR Rr 1 2 r Rr rr Figure 9.18-s3 Incomplete dominance in snapdragons (step 3)

Incomplete Dominance in Plants and People Hypercholesterolemia is a human trait that is an example of incomplete dominance and is characterized by dangerously high levels of cholesterol in the blood. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. As these variations of Mendel’s laws are introduced, students are likely to get confused and become uncertain about the prior definitions. Consider keeping a clear definition of these different patterns of inheritance available for the class to refer to as new patterns are discussed (perhaps as a handout for student reference). 2. As your class size increases, the chances increase that at least one student will have a family member with one of the genetic disorders discussed. Some students may find this embarrassing, but others might have a special interest in learning more about these topics, and may even be willing to share some of their family’s experiences with the class. Teaching Tips 1. Incomplete dominance is analogous to a compromise, or a shade of gray. The key concept is that both “sides” have input. Complete dominance is more analogous to an authoritarian style, overruling others and insisting on things being a certain way. Although these analogies might seem obvious to us, many students new to genetics appreciate them. 2. Another analogy for cholesterol receptors is fishing poles. The more fishing poles you use, the more fish you will likely catch. Heterozygotes for hypercholesterolemia have fewer “fishing poles” for cholesterol. Thus, fewer “fish” are caught and more “fish” remain in the water. 3. Students can think of blood types as analogous to socks on their feet. You can have socks that match, a sock on one foot but not the other, you can wear two socks that do not match, or you can even go barefoot (type O blood)! Developed further, think of amber (A) and blue (B) socks. Type A blood can have an amber sock with either another amber sock or a bare foot (or “zero” sock). Blue socks work the same way. One amber and one blue sock represent the AB blood type. Having no socks, as already noted, represents type O. 4. Consider specifically comparing the principles of codominance (expression of both alleles) and incomplete dominance (expression of one intermediate trait). Students will likely benefit from this direct comparison. 5. The American Sickle Cell Anemia Association’s website (www.ascaa.org) is a good place to get additional details. 6. Polygenic inheritance makes it possible for children to inherit genes to be taller, or shorter, than either parent. Similarly, skin tones can be darker or lighter than either parent. The environment also contributes significantly to the final phenotype for both of these traits. 7. The authors note that polygenic inheritance is the converse of pleiotropy. This is worth noting in lecture as these concepts are discussed. We often remember concepts better when they are contrasted in pairs. 8. As the authors are careful to note, although genetics and the environment both contribute to the final phenotypes, only the genetic factors are inherited. This distinction is important to understanding the limitations of Lamarck’s mechanisms of evolution. If you will address principles of evolution soon after this chapter, this may be an important distinction to reinforce in lecture. References to tattoos, piercing, and circumcision may also help to distinguish between environmental influences and inheritance. Students with tattoos will not produce children born with tattoos! And for thousands of years, fathers who are circumcised have not fathered boys also circumcised! Active Lecture Tips 1. See the activity Who Wants to Be a Millionaire? Inheritance on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 88

Incomplete Dominance in Plants and People In hypercholesterolemia, heterozygotes have blood cholesterol levels about twice normal, while homozygotes have about five times the normal amount of blood cholesterol and may have heart attacks as early as age 2. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. As these variations of Mendel’s laws are introduced, students are likely to get confused and become uncertain about the prior definitions. Consider keeping a clear definition of these different patterns of inheritance available for the class to refer to as new patterns are discussed (perhaps as a handout for student reference). 2. As your class size increases, the chances increase that at least one student will have a family member with one of the genetic disorders discussed. Some students may find this embarrassing, but others might have a special interest in learning more about these topics, and may even be willing to share some of their family’s experiences with the class. Teaching Tips 1. Incomplete dominance is analogous to a compromise, or a shade of gray. The key concept is that both “sides” have input. Complete dominance is more analogous to an authoritarian style, overruling others and insisting on things being a certain way. Although these analogies might seem obvious to us, many students new to genetics appreciate them. 2. Another analogy for cholesterol receptors is fishing poles. The more fishing poles you use, the more fish you will likely catch. Heterozygotes for hypercholesterolemia have fewer “fishing poles” for cholesterol. Thus, fewer “fish” are caught and more “fish” remain in the water. 3. Students can think of blood types as analogous to socks on their feet. You can have socks that match, a sock on one foot but not the other, you can wear two socks that do not match, or you can even go barefoot (type O blood)! Developed further, think of amber (A) and blue (B) socks. Type A blood can have an amber sock with either another amber sock or a bare foot (or “zero” sock). Blue socks work the same way. One amber and one blue sock represent the AB blood type. Having no socks, as already noted, represents type O. 4. Consider specifically comparing the principles of codominance (expression of both alleles) and incomplete dominance (expression of one intermediate trait). Students will likely benefit from this direct comparison. 5. The American Sickle Cell Anemia Association’s website (www.ascaa.org) is a good place to get additional details. 6. Polygenic inheritance makes it possible for children to inherit genes to be taller, or shorter, than either parent. Similarly, skin tones can be darker or lighter than either parent. The environment also contributes significantly to the final phenotype for both of these traits. 7. The authors note that polygenic inheritance is the converse of pleiotropy. This is worth noting in lecture as these concepts are discussed. We often remember concepts better when they are contrasted in pairs. 8. As the authors are careful to note, although genetics and the environment both contribute to the final phenotypes, only the genetic factors are inherited. This distinction is important to understanding the limitations of Lamarck’s mechanisms of evolution. If you will address principles of evolution soon after this chapter, this may be an important distinction to reinforce in lecture. References to tattoos, piercing, and circumcision may also help to distinguish between environmental influences and inheritance. Students with tattoos will not produce children born with tattoos! And for thousands of years, fathers who are circumcised have not fathered boys also circumcised! Active Lecture Tips 1. See the activity Who Wants to Be a Millionaire? Inheritance on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 89

HH Homozygous for ability to make LDL receptors Hh Heterozygous hh Figure 9.19 HH Homozygous for ability to make LDL receptors Hh Heterozygous hh Homozygous for inability to make LDL receptors GENOTYPE LDL LDL receptor PHENOTYPE Cell Normal Mild disease Severe disease Figure 9.19 Incomplete dominance in human hypercholesterolemia

ABO Blood Groups: An Example of Multiple Alleles and Codominance The ABO blood groups in humans involve three alleles of a single gene. Various combinations of these three alleles produce four phenotypes: A person’s blood type may be A, B, AB, or O. These letters refer to two carbohydrates, designated A and B, that may be found on the surface of red blood cells. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. As these variations of Mendel’s laws are introduced, students are likely to get confused and become uncertain about the prior definitions. Consider keeping a clear definition of these different patterns of inheritance available for the class to refer to as new patterns are discussed (perhaps as a handout for student reference). 2. As your class size increases, the chances increase that at least one student will have a family member with one of the genetic disorders discussed. Some students may find this embarrassing, but others might have a special interest in learning more about these topics, and may even be willing to share some of their family’s experiences with the class. Teaching Tips 1. Incomplete dominance is analogous to a compromise, or a shade of gray. The key concept is that both “sides” have input. Complete dominance is more analogous to an authoritarian style, overruling others and insisting on things being a certain way. Although these analogies might seem obvious to us, many students new to genetics appreciate them. 2. Another analogy for cholesterol receptors is fishing poles. The more fishing poles you use, the more fish you will likely catch. Heterozygotes for hypercholesterolemia have fewer “fishing poles” for cholesterol. Thus, fewer “fish” are caught and more “fish” remain in the water. 3. Students can think of blood types as analogous to socks on their feet. You can have socks that match, a sock on one foot but not the other, you can wear two socks that do not match, or you can even go barefoot (type O blood)! Developed further, think of amber (A) and blue (B) socks. Type A blood can have an amber sock with either another amber sock or a bare foot (or “zero” sock). Blue socks work the same way. One amber and one blue sock represent the AB blood type. Having no socks, as already noted, represents type O. 4. Consider specifically comparing the principles of codominance (expression of both alleles) and incomplete dominance (expression of one intermediate trait). Students will likely benefit from this direct comparison. 5. The American Sickle Cell Anemia Association’s website (www.ascaa.org) is a good place to get additional details. 6. Polygenic inheritance makes it possible for children to inherit genes to be taller, or shorter, than either parent. Similarly, skin tones can be darker or lighter than either parent. The environment also contributes significantly to the final phenotype for both of these traits. 7. The authors note that polygenic inheritance is the converse of pleiotropy. This is worth noting in lecture as these concepts are discussed. We often remember concepts better when they are contrasted in pairs. 8. As the authors are careful to note, although genetics and the environment both contribute to the final phenotypes, only the genetic factors are inherited. This distinction is important to understanding the limitations of Lamarck’s mechanisms of evolution. If you will address principles of evolution soon after this chapter, this may be an important distinction to reinforce in lecture. References to tattoos, piercing, and circumcision may also help to distinguish between environmental influences and inheritance. Students with tattoos will not produce children born with tattoos! And for thousands of years, fathers who are circumcised have not fathered boys also circumcised! Active Lecture Tips 1. See the activity Who Wants to Be a Millionaire? Inheritance on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 91

ii Blood Group (Pheno- type) Reactions When Blood from Groups Figure 9.20 Blood Group (Pheno- type) Reactions When Blood from Groups Below Is Mixed with Antibodies from Groups at Left Antibodies Present in Blood Genotypes Red Blood Cells O A B AB Carbohydrate A IA IA A or Anti-B IAi Carbohydrate B IB IB B or Anti-A IB i AB IA IB Anti-A Anti-B O ii Figure 9.20 Multiple alleles for the ABO blood groups

Carbohydrate A or Carbohydrate B Figure 9.20-1 Blood Group (Pheno- type) Antibodies Present in Blood Genotypes Red Blood Cells Carbohydrate A I A I A A Anti-B or I A i Carbohydrate B I B I B B Anti-A or I B i AB I A I B Anti-A Anti-B O ii Figure 9.20-1 Multiple alleles for the ABO blood groups (part 1: genotypes and antibodies)

Reactions When Blood from Groups Below Is Mixed with Antibodies from Figure 9.20-2 Blood Group (Pheno- type) Reactions When Blood from Groups Below Is Mixed with Antibodies from Groups at Left O A B AB A B AB O Figure 9.20-2 Multiple alleles for the ABO blood groups (part 2: reactions)

Figure 9.20-3 Figure 9.20-3 Multiple alleles for the ABO blood groups (part 3: blood-typing photo)

ABO Blood Groups: An Example of Multiple Alleles and Codominance Matching compatible blood groups is critical for safe blood transfusions. If a donor’s blood cells have a carbohydrate (A or B) that is foreign to the recipient, then the recipient’s immune system produces blood proteins called antibodies that bind to the foreign carbohydrates and cause the donor blood cells to clump together, potentially killing the recipient. © 2016 Pearson Education, Inc.

ABO Blood Groups: An Example of Multiple Alleles and Codominance The four blood groups result from various combinations of the three different alleles: IA (for the ability to make substance A), IB (for B), and i (for neither A nor B). Each person inherits one of these alleles from each parent. © 2016 Pearson Education, Inc.

ABO Blood Groups: An Example of Multiple Alleles and Codominance Because there are three alleles, there are six possible genotypes, as listed in Figure 9.20. Both the IA and IB alleles are dominant to the i allele. People of genotype IAIB make both carbohydrates. In other words, the IA and IB alleles are codominant, meaning that both alleles are expressed in heterozygous individuals (IAIB) who have type AB blood. © 2016 Pearson Education, Inc.

Structure/Function: Pleiotropy and Sickle-Cell Disease Pleiotropy is when one gene influences several characters. Sickle-cell disease exhibits pleiotropy, results in abnormal hemoglobin proteins, and causes disk-shaped red blood cells to deform into a sickle shape with jagged edges. In most cases, only people who are homozygous for the sickle-cell allele have sickle-cell disease. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. As these variations of Mendel’s laws are introduced, students are likely to get confused and become uncertain about the prior definitions. Consider keeping a clear definition of these different patterns of inheritance available for the class to refer to as new patterns are discussed (perhaps as a handout for student reference). 2. As your class size increases, the chances increase that at least one student will have a family member with one of the genetic disorders discussed. Some students may find this embarrassing, but others might have a special interest in learning more about these topics, and may even be willing to share some of their family’s experiences with the class. Teaching Tips 1. Incomplete dominance is analogous to a compromise, or a shade of gray. The key concept is that both “sides” have input. Complete dominance is more analogous to an authoritarian style, overruling others and insisting on things being a certain way. Although these analogies might seem obvious to us, many students new to genetics appreciate them. 2. Another analogy for cholesterol receptors is fishing poles. The more fishing poles you use, the more fish you will likely catch. Heterozygotes for hypercholesterolemia have fewer “fishing poles” for cholesterol. Thus, fewer “fish” are caught and more “fish” remain in the water. 3. Students can think of blood types as analogous to socks on their feet. You can have socks that match, a sock on one foot but not the other, you can wear two socks that do not match, or you can even go barefoot (type O blood)! Developed further, think of amber (A) and blue (B) socks. Type A blood can have an amber sock with either another amber sock or a bare foot (or “zero” sock). Blue socks work the same way. One amber and one blue sock represent the AB blood type. Having no socks, as already noted, represents type O. 4. Consider specifically comparing the principles of codominance (expression of both alleles) and incomplete dominance (expression of one intermediate trait). Students will likely benefit from this direct comparison. 5. The American Sickle Cell Anemia Association’s website (www.ascaa.org) is a good place to get additional details. 6. Polygenic inheritance makes it possible for children to inherit genes to be taller, or shorter, than either parent. Similarly, skin tones can be darker or lighter than either parent. The environment also contributes significantly to the final phenotype for both of these traits. 7. The authors note that polygenic inheritance is the converse of pleiotropy. This is worth noting in lecture as these concepts are discussed. We often remember concepts better when they are contrasted in pairs. 8. As the authors are careful to note, although genetics and the environment both contribute to the final phenotypes, only the genetic factors are inherited. This distinction is important to understanding the limitations of Lamarck’s mechanisms of evolution. If you will address principles of evolution soon after this chapter, this may be an important distinction to reinforce in lecture. References to tattoos, piercing, and circumcision may also help to distinguish between environmental influences and inheritance. Students with tattoos will not produce children born with tattoos! And for thousands of years, fathers who are circumcised have not fathered boys also circumcised! Active Lecture Tips 1. See the activity Who Wants to Be a Millionaire? Inheritance on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 99

Individual homozygous for sickle-cell allele Figure 9.21 Individual homozygous for sickle-cell allele Sickle-cell (abnormal) hemoglobin Abnormal hemoglobin crystallizes into long, flexible chains, causing red blood cells to become sickle-shaped. Colorized SEM Sickled cells can lead to a cascade of symptoms, such as weakness, pain, organ damage, and paralysis. Figure 9.21 Sickle-cell disease: multiple effects of a single human gene

Figure 9.21-1 Colorized SEM Figure 9.21-1 Sickle-cell disease: multiple effects of a single human gene (part 1: SEM)

Polygenic Inheritance Polygenic inheritance is the additive effects of two or more genes on a single phenotypic character and the logical opposite of pleiotropy, in which one gene affects several characters. There is evidence that height in people is controlled by several genes that are inherited separately. (Actually, human height is probably affected by a great number of genes, but we’ll simplify here.) © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. As these variations of Mendel’s laws are introduced, students are likely to get confused and become uncertain about the prior definitions. Consider keeping a clear definition of these different patterns of inheritance available for the class to refer to as new patterns are discussed (perhaps as a handout for student reference). 2. As your class size increases, the chances increase that at least one student will have a family member with one of the genetic disorders discussed. Some students may find this embarrassing, but others might have a special interest in learning more about these topics, and may even be willing to share some of their family’s experiences with the class. Teaching Tips 1. Incomplete dominance is analogous to a compromise, or a shade of gray. The key concept is that both “sides” have input. Complete dominance is more analogous to an authoritarian style, overruling others and insisting on things being a certain way. Although these analogies might seem obvious to us, many students new to genetics appreciate them. 2. Another analogy for cholesterol receptors is fishing poles. The more fishing poles you use, the more fish you will likely catch. Heterozygotes for hypercholesterolemia have fewer “fishing poles” for cholesterol. Thus, fewer “fish” are caught and more “fish” remain in the water. 3. Students can think of blood types as analogous to socks on their feet. You can have socks that match, a sock on one foot but not the other, you can wear two socks that do not match, or you can even go barefoot (type O blood)! Developed further, think of amber (A) and blue (B) socks. Type A blood can have an amber sock with either another amber sock or a bare foot (or “zero” sock). Blue socks work the same way. One amber and one blue sock represent the AB blood type. Having no socks, as already noted, represents type O. 4. Consider specifically comparing the principles of codominance (expression of both alleles) and incomplete dominance (expression of one intermediate trait). Students will likely benefit from this direct comparison. 5. The American Sickle Cell Anemia Association’s website (www.ascaa.org) is a good place to get additional details. 6. Polygenic inheritance makes it possible for children to inherit genes to be taller, or shorter, than either parent. Similarly, skin tones can be darker or lighter than either parent. The environment also contributes significantly to the final phenotype for both of these traits. 7. The authors note that polygenic inheritance is the converse of pleiotropy. This is worth noting in lecture as these concepts are discussed. We often remember concepts better when they are contrasted in pairs. 8. As the authors are careful to note, although genetics and the environment both contribute to the final phenotypes, only the genetic factors are inherited. This distinction is important to understanding the limitations of Lamarck’s mechanisms of evolution. If you will address principles of evolution soon after this chapter, this may be an important distinction to reinforce in lecture. References to tattoos, piercing, and circumcision may also help to distinguish between environmental influences and inheritance. Students with tattoos will not produce children born with tattoos! And for thousands of years, fathers who are circumcised have not fathered boys also circumcised! Active Lecture Tips 1. See the activity Who Wants to Be a Millionaire? Inheritance on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 102

Fraction of population Figure 9.22 P Generation = short allele = tall allele aabbcc (very short) AABBCC (very tall) F1 Generation AaBbCc (medium height) AaBbCc (medium height) F2 Generation Sperm 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 20 64 1 8 1 8 15 64 1 8 Eggs 1 8 Fraction of population 1 8 6 64 1 8 1 8 1 64 Adult height 1 64 6 64 15 64 20 64 15 64 6 64 1 64 Very short Very tall Figure 9.22 A model for polygenic inheritance of height

P Generation = short allele = tall allele aabbcc AABBCC (very short) Figure 9.22-1 P Generation = short allele = tall allele aabbcc (very short) AABBCC (very tall) F1 Generation AaBbCc (medium height) AaBbCc (medium height) Figure 9.22-1 A model for polygenic inheritance of height (part 1: P and F1 generations)

F2 Generation Sperm Eggs = short allele = tall allele 1 8 1 8 1 8 1 8 Figure 9.22-2 F2 Generation Sperm 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 Eggs 1 8 1 8 1 8 1 8 = short allele 1 64 6 64 15 64 20 64 15 64 6 64 1 64 = tall allele Figure 9.22-2 A model for polygenic inheritance of height (part 2: F2 generation)

Fraction of population Figure 9.22-3 20 64 15 64 Fraction of population 6 64 1 64 Adult height Very short Very tall Figure 9.22-3 A model for polygenic inheritance of height (part 3: bell curve)

Epigenetics and the Role of Environment Many phenotypic characters result from a combination of heredity and environment. Whether human characters are more influenced by genes or by the environment—nature or nurture—is a very old and hotly contested issue. Spending time with identical twins will convince anyone that environment, and not just genes, affects a person’s traits. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. As these variations of Mendel’s laws are introduced, students are likely to get confused and become uncertain about the prior definitions. Consider keeping a clear definition of these different patterns of inheritance available for the class to refer to as new patterns are discussed (perhaps as a handout for student reference). 2. As your class size increases, the chances increase that at least one student will have a family member with one of the genetic disorders discussed. Some students may find this embarrassing, but others might have a special interest in learning more about these topics, and may even be willing to share some of their family’s experiences with the class. Teaching Tips 1. Incomplete dominance is analogous to a compromise, or a shade of gray. The key concept is that both “sides” have input. Complete dominance is more analogous to an authoritarian style, overruling others and insisting on things being a certain way. Although these analogies might seem obvious to us, many students new to genetics appreciate them. 2. Another analogy for cholesterol receptors is fishing poles. The more fishing poles you use, the more fish you will likely catch. Heterozygotes for hypercholesterolemia have fewer “fishing poles” for cholesterol. Thus, fewer “fish” are caught and more “fish” remain in the water. 3. Students can think of blood types as analogous to socks on their feet. You can have socks that match, a sock on one foot but not the other, you can wear two socks that do not match, or you can even go barefoot (type O blood)! Developed further, think of amber (A) and blue (B) socks. Type A blood can have an amber sock with either another amber sock or a bare foot (or “zero” sock). Blue socks work the same way. One amber and one blue sock represent the AB blood type. Having no socks, as already noted, represents type O. 4. Consider specifically comparing the principles of codominance (expression of both alleles) and incomplete dominance (expression of one intermediate trait). Students will likely benefit from this direct comparison. 5. The American Sickle Cell Anemia Association’s website (www.ascaa.org) is a good place to get additional details. 6. Polygenic inheritance makes it possible for children to inherit genes to be taller, or shorter, than either parent. Similarly, skin tones can be darker or lighter than either parent. The environment also contributes significantly to the final phenotype for both of these traits. 7. The authors note that polygenic inheritance is the converse of pleiotropy. This is worth noting in lecture as these concepts are discussed. We often remember concepts better when they are contrasted in pairs. 8. As the authors are careful to note, although genetics and the environment both contribute to the final phenotypes, only the genetic factors are inherited. This distinction is important to understanding the limitations of Lamarck’s mechanisms of evolution. If you will address principles of evolution soon after this chapter, this may be an important distinction to reinforce in lecture. References to tattoos, piercing, and circumcision may also help to distinguish between environmental influences and inheritance. Students with tattoos will not produce children born with tattoos! And for thousands of years, fathers who are circumcised have not fathered boys also circumcised! Active Lecture Tips 1. See the activity Who Wants to Be a Millionaire? Inheritance on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 107

Figure 9.23-1 Figure 9.23-1 As a result of environmental influences, even identical twins can look different (part 1: identical twins)

Figure 9.23-2 Figure 9.23-2 As a result of environmental influences, even identical twins can look different (part 2: genetically identical leaves)

Epigenetics and the Role of Environment In general, only genetic influences are inherited and effects of the environment are not passed to the next generation. In recent years, however, biologists have begun to recognize the importance of epigenetic inheritance, the transmission of traits by mechanisms not directly involving DNA sequence. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. As these variations of Mendel’s laws are introduced, students are likely to get confused and become uncertain about the prior definitions. Consider keeping a clear definition of these different patterns of inheritance available for the class to refer to as new patterns are discussed (perhaps as a handout for student reference). 2. As your class size increases, the chances increase that at least one student will have a family member with one of the genetic disorders discussed. Some students may find this embarrassing, but others might have a special interest in learning more about these topics, and may even be willing to share some of their family’s experiences with the class. Teaching Tips 1. Incomplete dominance is analogous to a compromise, or a shade of gray. The key concept is that both “sides” have input. Complete dominance is more analogous to an authoritarian style, overruling others and insisting on things being a certain way. Although these analogies might seem obvious to us, many students new to genetics appreciate them. 2. Another analogy for cholesterol receptors is fishing poles. The more fishing poles you use, the more fish you will likely catch. Heterozygotes for hypercholesterolemia have fewer “fishing poles” for cholesterol. Thus, fewer “fish” are caught and more “fish” remain in the water. 3. Students can think of blood types as analogous to socks on their feet. You can have socks that match, a sock on one foot but not the other, you can wear two socks that do not match, or you can even go barefoot (type O blood)! Developed further, think of amber (A) and blue (B) socks. Type A blood can have an amber sock with either another amber sock or a bare foot (or “zero” sock). Blue socks work the same way. One amber and one blue sock represent the AB blood type. Having no socks, as already noted, represents type O. 4. Consider specifically comparing the principles of codominance (expression of both alleles) and incomplete dominance (expression of one intermediate trait). Students will likely benefit from this direct comparison. 5. The American Sickle Cell Anemia Association’s website (www.ascaa.org) is a good place to get additional details. 6. Polygenic inheritance makes it possible for children to inherit genes to be taller, or shorter, than either parent. Similarly, skin tones can be darker or lighter than either parent. The environment also contributes significantly to the final phenotype for both of these traits. 7. The authors note that polygenic inheritance is the converse of pleiotropy. This is worth noting in lecture as these concepts are discussed. We often remember concepts better when they are contrasted in pairs. 8. As the authors are careful to note, although genetics and the environment both contribute to the final phenotypes, only the genetic factors are inherited. This distinction is important to understanding the limitations of Lamarck’s mechanisms of evolution. If you will address principles of evolution soon after this chapter, this may be an important distinction to reinforce in lecture. References to tattoos, piercing, and circumcision may also help to distinguish between environmental influences and inheritance. Students with tattoos will not produce children born with tattoos! And for thousands of years, fathers who are circumcised have not fathered boys also circumcised! Active Lecture Tips 1. See the activity Who Wants to Be a Millionaire? Inheritance on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 110

Epigenetics and the Role of Environment For example, components of chromosomes can be chemically modified by adding or removing chemical groups on the DNA and/or protein components of chromosomes. Over a lifetime, the environment plays a role in these changes, which may explain how one identical twin can suffer from a genetically based disease whereas the other twin does not, despite their identical genomes. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. As these variations of Mendel’s laws are introduced, students are likely to get confused and become uncertain about the prior definitions. Consider keeping a clear definition of these different patterns of inheritance available for the class to refer to as new patterns are discussed (perhaps as a handout for student reference). 2. As your class size increases, the chances increase that at least one student will have a family member with one of the genetic disorders discussed. Some students may find this embarrassing, but others might have a special interest in learning more about these topics, and may even be willing to share some of their family’s experiences with the class. Teaching Tips 1. Incomplete dominance is analogous to a compromise, or a shade of gray. The key concept is that both “sides” have input. Complete dominance is more analogous to an authoritarian style, overruling others and insisting on things being a certain way. Although these analogies might seem obvious to us, many students new to genetics appreciate them. 2. Another analogy for cholesterol receptors is fishing poles. The more fishing poles you use, the more fish you will likely catch. Heterozygotes for hypercholesterolemia have fewer “fishing poles” for cholesterol. Thus, fewer “fish” are caught and more “fish” remain in the water. 3. Students can think of blood types as analogous to socks on their feet. You can have socks that match, a sock on one foot but not the other, you can wear two socks that do not match, or you can even go barefoot (type O blood)! Developed further, think of amber (A) and blue (B) socks. Type A blood can have an amber sock with either another amber sock or a bare foot (or “zero” sock). Blue socks work the same way. One amber and one blue sock represent the AB blood type. Having no socks, as already noted, represents type O. 4. Consider specifically comparing the principles of codominance (expression of both alleles) and incomplete dominance (expression of one intermediate trait). Students will likely benefit from this direct comparison. 5. The American Sickle Cell Anemia Association’s website (www.ascaa.org) is a good place to get additional details. 6. Polygenic inheritance makes it possible for children to inherit genes to be taller, or shorter, than either parent. Similarly, skin tones can be darker or lighter than either parent. The environment also contributes significantly to the final phenotype for both of these traits. 7. The authors note that polygenic inheritance is the converse of pleiotropy. This is worth noting in lecture as these concepts are discussed. We often remember concepts better when they are contrasted in pairs. 8. As the authors are careful to note, although genetics and the environment both contribute to the final phenotypes, only the genetic factors are inherited. This distinction is important to understanding the limitations of Lamarck’s mechanisms of evolution. If you will address principles of evolution soon after this chapter, this may be an important distinction to reinforce in lecture. References to tattoos, piercing, and circumcision may also help to distinguish between environmental influences and inheritance. Students with tattoos will not produce children born with tattoos! And for thousands of years, fathers who are circumcised have not fathered boys also circumcised! Active Lecture Tips 1. See the activity Who Wants to Be a Millionaire? Inheritance on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 111

Epigenetics and the Role of Environment Epigenetic modifications—and the changes in gene activity that result—may even be carried on to the next generation. Unlike alterations to the DNA sequence, chemical changes to the chromosomes can be reversed. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. As these variations of Mendel’s laws are introduced, students are likely to get confused and become uncertain about the prior definitions. Consider keeping a clear definition of these different patterns of inheritance available for the class to refer to as new patterns are discussed (perhaps as a handout for student reference). 2. As your class size increases, the chances increase that at least one student will have a family member with one of the genetic disorders discussed. Some students may find this embarrassing, but others might have a special interest in learning more about these topics, and may even be willing to share some of their family’s experiences with the class. Teaching Tips 1. Incomplete dominance is analogous to a compromise, or a shade of gray. The key concept is that both “sides” have input. Complete dominance is more analogous to an authoritarian style, overruling others and insisting on things being a certain way. Although these analogies might seem obvious to us, many students new to genetics appreciate them. 2. Another analogy for cholesterol receptors is fishing poles. The more fishing poles you use, the more fish you will likely catch. Heterozygotes for hypercholesterolemia have fewer “fishing poles” for cholesterol. Thus, fewer “fish” are caught and more “fish” remain in the water. 3. Students can think of blood types as analogous to socks on their feet. You can have socks that match, a sock on one foot but not the other, you can wear two socks that do not match, or you can even go barefoot (type O blood)! Developed further, think of amber (A) and blue (B) socks. Type A blood can have an amber sock with either another amber sock or a bare foot (or “zero” sock). Blue socks work the same way. One amber and one blue sock represent the AB blood type. Having no socks, as already noted, represents type O. 4. Consider specifically comparing the principles of codominance (expression of both alleles) and incomplete dominance (expression of one intermediate trait). Students will likely benefit from this direct comparison. 5. The American Sickle Cell Anemia Association’s website (www.ascaa.org) is a good place to get additional details. 6. Polygenic inheritance makes it possible for children to inherit genes to be taller, or shorter, than either parent. Similarly, skin tones can be darker or lighter than either parent. The environment also contributes significantly to the final phenotype for both of these traits. 7. The authors note that polygenic inheritance is the converse of pleiotropy. This is worth noting in lecture as these concepts are discussed. We often remember concepts better when they are contrasted in pairs. 8. As the authors are careful to note, although genetics and the environment both contribute to the final phenotypes, only the genetic factors are inherited. This distinction is important to understanding the limitations of Lamarck’s mechanisms of evolution. If you will address principles of evolution soon after this chapter, this may be an important distinction to reinforce in lecture. References to tattoos, piercing, and circumcision may also help to distinguish between environmental influences and inheritance. Students with tattoos will not produce children born with tattoos! And for thousands of years, fathers who are circumcised have not fathered boys also circumcised! Active Lecture Tips 1. See the activity Who Wants to Be a Millionaire? Inheritance on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 112

The Chromosomal Basis of Inheritance The chromosome theory of inheritance states that genes are located at specific positions (loci) on chromosomes and the behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. This section of the chapter relies on a good understanding of the chromosome sorting process of meiosis. If students were not assigned Chapter 8, and meiosis was not otherwise addressed, it will be difficult for students to understand the chromosomal basis of inheritance or linked genes. 2. The nature of linked genes builds on our natural expectations that items that are closer together are less likely to be separated. Yet students may find such concepts initially foreign. Whether it is parents holding the hands of children or people and their pets, we generally know that separation is more likely when things are farther apart. You might demonstrate this simply by drawing a line down a page of text. The likelihood that the line separates any pair of words increases, as the distance between the words grows farther apart. 3. The discussion of “linked genes” addresses a different relationship than the use of the similar termed “sex-linked genes.” The nature of the linkage is quite different. Consider emphasizing this distinction for your students. 4. The likelihood that at least some students are colorblind in larger classes is very high. Some of these students might find this interesting and want to discuss it further. However, others might be embarrassed by what might be perceived as a defect. Teaching Tips 1. Building on the shoe analogy developed in Chapter 8, linked genes are like a shoe and its shoelaces. The two are usually transferred together but can be moved separately under special circumstances. 2. Crossing over (from Chapter 8) is like randomly editing out a minute of film from two movies and swapping them. Perhaps the fifth minute of Bambi is swapped for the fifth minute of a Shrek film. Clearly, the closer that two frames of film are together, the more likely they are to move or remain together. 3. In some ways, sex-linked genes reflect the risk of not having a backup copy of a file on your computer. If you only have one copy and it is damaged, you have to live with the damaged file. Having two X chromosomes in females provides a “backup copy” that can function if one of the sex-linked genes is damaged. 4. Hemophilia and other genetic diseases may also result from spontaneous mutations in a family with no known history of the disease. Although rare, this possibility should always be considered when tracing the history of an inherited disease. 5. Female hemophiliacs are very rare because both X chromosomes would need to have the recessive trait. Although very unlikely, female hemophiliacs are known. Students may enjoy searching for details of these rare cases. For additional information about hemophilia, consider visiting the website of the National Hemophilia Foundation at www.hemophilia.org. Active Lecture Tips 1. See the activity Pairs of Shoes and Pairs of Chromosomes on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 2. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 113

The Chromosomal Basis of Inheritance It is chromosomes that undergo segregation and independent assortment during meiosis and account for Mendel’s laws. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. This section of the chapter relies on a good understanding of the chromosome sorting process of meiosis. If students were not assigned Chapter 8, and meiosis was not otherwise addressed, it will be difficult for students to understand the chromosomal basis of inheritance or linked genes. 2. The nature of linked genes builds on our natural expectations that items that are closer together are less likely to be separated. Yet students may find such concepts initially foreign. Whether it is parents holding the hands of children or people and their pets, we generally know that separation is more likely when things are farther apart. You might demonstrate this simply by drawing a line down a page of text. The likelihood that the line separates any pair of words increases, as the distance between the words grows farther apart. 3. The discussion of “linked genes” addresses a different relationship than the use of the similar termed “sex-linked genes.” The nature of the linkage is quite different. Consider emphasizing this distinction for your students. 4. The likelihood that at least some students are colorblind in larger classes is very high. Some of these students might find this interesting and want to discuss it further. However, others might be embarrassed by what might be perceived as a defect. Teaching Tips 1. Building on the shoe analogy developed in Chapter 8, linked genes are like a shoe and its shoelaces. The two are usually transferred together but can be moved separately under special circumstances. 2. Crossing over (from Chapter 8) is like randomly editing out a minute of film from two movies and swapping them. Perhaps the fifth minute of Bambi is swapped for the fifth minute of a Shrek film. Clearly, the closer that two frames of film are together, the more likely they are to move or remain together. 3. In some ways, sex-linked genes reflect the risk of not having a backup copy of a file on your computer. If you only have one copy and it is damaged, you have to live with the damaged file. Having two X chromosomes in females provides a “backup copy” that can function if one of the sex-linked genes is damaged. 4. Hemophilia and other genetic diseases may also result from spontaneous mutations in a family with no known history of the disease. Although rare, this possibility should always be considered when tracing the history of an inherited disease. 5. Female hemophiliacs are very rare because both X chromosomes would need to have the recessive trait. Although very unlikely, female hemophiliacs are known. Students may enjoy searching for details of these rare cases. For additional information about hemophilia, consider visiting the website of the National Hemophilia Foundation at www.hemophilia.org. Active Lecture Tips 1. See the activity Pairs of Shoes and Pairs of Chromosomes on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 2. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 114

All round-yellow seeds Figure 9.24 P Generation Round-yellow seeds (RRYY) Wrinkled-green Seeds (rryy) y Y r R Y R y r MEIOSIS FERTILIZATION Gametes R Y y r F1 Generation All round-yellow seeds (RrYy) R Law of Segregation: Follow the long chromosomes. r y Law of Independent Assortment: Follow both the long and the short chromosomes. Y MEIOSIS R r r R Metaphase I (alternative arrangements) They are arranged in either of two equally likely ways at metaphase I. The R and r alleles segregate in anaphase I. Y y Y y R r Metaphase II r R Only one long chromosome ends up in each gamete. They sort independently, giving four gamete types. Y y Y y y Y Y y Y Y y y Gametes R R r r r r R R 1 4 RY 1 4 ry 1 4 rY 1 4 Ry Fertilization results in the 9:3:3:1 phenotypic ratio in the F2 generation. Fertilization recombines the r and R alleles at random. FERTILIZATION AMONG THE F1 PLANTS F2 Generation 9 : 3 : 3 :1 Figure 9.24 The chromosomal basis of Mendel’s laws

All round-yellow seeds Figure 9.24-1 P Generation Round-yellow seeds (RRYY) Wrinkled-green seeds (rryy) y Y r R Y r R y MEIOSIS FERTILIZATION Gametes y r R Y F1 Generation All round-yellow seeds (RrYy) R y r Y Figure 9.24-1 The chromosomal basis of Mendel’s laws (part 1: P generation meiosis)

All round-yellow seeds (RrYy) Figure 9.24-2 F1 Generation All round-yellow seeds (RrYy) R Law of Segregation: Follow the long chromosomes. y Law of Independent Assortment: Follow both the long and the short chromosomes. r Y MEIOSIS R r r R They are arranged in either of two equally likely ways at metaphase I. The R and r alleles segregate in anaphase I. Y y Y y MEIOSIS R r r R Only one long chromosome ends up in each gamete. They sort independently, giving four gamete types. Y y Y y Y y Y y Y Y y y R R r r r r R R 1 4 RY 1 4 ry 1 4 rY 1 4 Ry Fertilization recombines the r and R alleles at random. Fertilization results in the 9:3:3:1 phenotypic ratio in the F2 generation. Figure 9.24-2 The chromosomal basis of Mendel’s laws (part 2: F1 generation meiosis)

Linked Genes Linked genes are located near each other on the same chromosome and tend to travel together during meiosis and fertilization. Such genes are often inherited as a set and therefore often do not follow Mendel’s law of independent assortment. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. This section of the chapter relies on a good understanding of the chromosome sorting process of meiosis. If students were not assigned Chapter 8, and meiosis was not otherwise addressed, it will be difficult for students to understand the chromosomal basis of inheritance or linked genes. 2. The nature of linked genes builds on our natural expectations that items that are closer together are less likely to be separated. Yet students may find such concepts initially foreign. Whether it is parents holding the hands of children or people and their pets, we generally know that separation is more likely when things are farther apart. You might demonstrate this simply by drawing a line down a page of text. The likelihood that the line separates any pair of words increases, as the distance between the words grows farther apart. 3. The discussion of “linked genes” addresses a different relationship than the use of the similar termed “sex-linked genes.” The nature of the linkage is quite different. Consider emphasizing this distinction for your students. 4. The likelihood that at least some students are colorblind in larger classes is very high. Some of these students might find this interesting and want to discuss it further. However, others might be embarrassed by what might be perceived as a defect. Teaching Tips 1. Building on the shoe analogy developed in Chapter 8, linked genes are like a shoe and its shoelaces. The two are usually transferred together but can be moved separately under special circumstances. 2. Crossing over (from Chapter 8) is like randomly editing out a minute of film from two movies and swapping them. Perhaps the fifth minute of Bambi is swapped for the fifth minute of a Shrek film. Clearly, the closer that two frames of film are together, the more likely they are to move or remain together. 3. In some ways, sex-linked genes reflect the risk of not having a backup copy of a file on your computer. If you only have one copy and it is damaged, you have to live with the damaged file. Having two X chromosomes in females provides a “backup copy” that can function if one of the sex-linked genes is damaged. 4. Hemophilia and other genetic diseases may also result from spontaneous mutations in a family with no known history of the disease. Although rare, this possibility should always be considered when tracing the history of an inherited disease. 5. Female hemophiliacs are very rare because both X chromosomes would need to have the recessive trait. Although very unlikely, female hemophiliacs are known. Students may enjoy searching for details of these rare cases. For additional information about hemophilia, consider visiting the website of the National Hemophilia Foundation at www.hemophilia.org. Active Lecture Tips 1. See the activity Pairs of Shoes and Pairs of Chromosomes on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 2. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 118

Sex Determination in Humans Many animals, including all mammals, have a pair of sex chromosomes, designated X and Y, that determine an individual’s sex. Individuals with one X chromosome and one Y chromosome are males. XX individuals are females. Human males and females both have 44 autosomes (chromosomes other than sex chromosomes). © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. This section of the chapter relies on a good understanding of the chromosome sorting process of meiosis. If students were not assigned Chapter 8, and meiosis was not otherwise addressed, it will be difficult for students to understand the chromosomal basis of inheritance or linked genes. 2. The nature of linked genes builds on our natural expectations that items that are closer together are less likely to be separated. Yet students may find such concepts initially foreign. Whether it is parents holding the hands of children or people and their pets, we generally know that separation is more likely when things are farther apart. You might demonstrate this simply by drawing a line down a page of text. The likelihood that the line separates any pair of words increases, as the distance between the words grows farther apart. 3. The discussion of “linked genes” addresses a different relationship than the use of the similar termed “sex-linked genes.” The nature of the linkage is quite different. Consider emphasizing this distinction for your students. 4. The likelihood that at least some students are colorblind in larger classes is very high. Some of these students might find this interesting and want to discuss it further. However, others might be embarrassed by what might be perceived as a defect. Teaching Tips 1. Building on the shoe analogy developed in Chapter 8, linked genes are like a shoe and its shoelaces. The two are usually transferred together but can be moved separately under special circumstances. 2. Crossing over (from Chapter 8) is like randomly editing out a minute of film from two movies and swapping them. Perhaps the fifth minute of Bambi is swapped for the fifth minute of a Shrek film. Clearly, the closer that two frames of film are together, the more likely they are to move or remain together. 3. In some ways, sex-linked genes reflect the risk of not having a backup copy of a file on your computer. If you only have one copy and it is damaged, you have to live with the damaged file. Having two X chromosomes in females provides a “backup copy” that can function if one of the sex-linked genes is damaged. 4. Hemophilia and other genetic diseases may also result from spontaneous mutations in a family with no known history of the disease. Although rare, this possibility should always be considered when tracing the history of an inherited disease. 5. Female hemophiliacs are very rare because both X chromosomes would need to have the recessive trait. Although very unlikely, female hemophiliacs are known. Students may enjoy searching for details of these rare cases. For additional information about hemophilia, consider visiting the website of the National Hemophilia Foundation at www.hemophilia.org. Active Lecture Tips 1. See the activity Pairs of Shoes and Pairs of Chromosomes on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 2. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 119

Male Female Somatic cells Y X Sperm Egg Offspring Female Male Figure 9.25 Male Female 44  XY Somatic cells 44  XX Y X Colorized SEM 22  X 22  Y 22  X Sperm Egg 44  XX 44  XY Offspring Female Male Figure 9.25 The chromosomal basis of sex determination in humans

Male Female Somatic cells Sperm Egg Offspring Female Male 44  XY 44  Figure 9.25-1 Male Female 44  XY Somatic cells 44  XX 22  X 22  Y 22  X Sperm Egg 44  XX 44  XY Offspring Female Male Figure 9.25-1 The chromosomal basis of sex determination in humans (part 1: diagram)

Y X Colorized SEM Figure 9.25-2 Figure 9.25-2 The chromosomal basis of sex determination in humans (part 2: SEM)

Sex-Linked Genes A gene located on a sex chromosome is called a sex-linked gene. Most sex-linked genes are found on the X chromosome. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. This section of the chapter relies on a good understanding of the chromosome sorting process of meiosis. If students were not assigned Chapter 8, and meiosis was not otherwise addressed, it will be difficult for students to understand the chromosomal basis of inheritance or linked genes. 2. The nature of linked genes builds on our natural expectations that items that are closer together are less likely to be separated. Yet students may find such concepts initially foreign. Whether it is parents holding the hands of children or people and their pets, we generally know that separation is more likely when things are farther apart. You might demonstrate this simply by drawing a line down a page of text. The likelihood that the line separates any pair of words increases, as the distance between the words grows farther apart. 3. The discussion of “linked genes” addresses a different relationship than the use of the similar termed “sex-linked genes.” The nature of the linkage is quite different. Consider emphasizing this distinction for your students. 4. The likelihood that at least some students are colorblind in larger classes is very high. Some of these students might find this interesting and want to discuss it further. However, others might be embarrassed by what might be perceived as a defect. Teaching Tips 1. Building on the shoe analogy developed in Chapter 8, linked genes are like a shoe and its shoelaces. The two are usually transferred together but can be moved separately under special circumstances. 2. Crossing over (from Chapter 8) is like randomly editing out a minute of film from two movies and swapping them. Perhaps the fifth minute of Bambi is swapped for the fifth minute of a Shrek film. Clearly, the closer that two frames of film are together, the more likely they are to move or remain together. 3. In some ways, sex-linked genes reflect the risk of not having a backup copy of a file on your computer. If you only have one copy and it is damaged, you have to live with the damaged file. Having two X chromosomes in females provides a “backup copy” that can function if one of the sex-linked genes is damaged. 4. Hemophilia and other genetic diseases may also result from spontaneous mutations in a family with no known history of the disease. Although rare, this possibility should always be considered when tracing the history of an inherited disease. 5. Female hemophiliacs are very rare because both X chromosomes would need to have the recessive trait. Although very unlikely, female hemophiliacs are known. Students may enjoy searching for details of these rare cases. For additional information about hemophilia, consider visiting the website of the National Hemophilia Foundation at www.hemophilia.org. Active Lecture Tips 1. See the activity Pairs of Shoes and Pairs of Chromosomes on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 2. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 123

Sex-Linked Genes A number of human conditions, including red-green colorblindness, hemophilia, and a type of muscular dystrophy, result from sex-linked recessive alleles. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. This section of the chapter relies on a good understanding of the chromosome sorting process of meiosis. If students were not assigned Chapter 8, and meiosis was not otherwise addressed, it will be difficult for students to understand the chromosomal basis of inheritance or linked genes. 2. The nature of linked genes builds on our natural expectations that items that are closer together are less likely to be separated. Yet students may find such concepts initially foreign. Whether it is parents holding the hands of children or people and their pets, we generally know that separation is more likely when things are farther apart. You might demonstrate this simply by drawing a line down a page of text. The likelihood that the line separates any pair of words increases, as the distance between the words grows farther apart. 3. The discussion of “linked genes” addresses a different relationship than the use of the similar termed “sex-linked genes.” The nature of the linkage is quite different. Consider emphasizing this distinction for your students. 4. The likelihood that at least some students are colorblind in larger classes is very high. Some of these students might find this interesting and want to discuss it further. However, others might be embarrassed by what might be perceived as a defect. Teaching Tips 1. Building on the shoe analogy developed in Chapter 8, linked genes are like a shoe and its shoelaces. The two are usually transferred together but can be moved separately under special circumstances. 2. Crossing over (from Chapter 8) is like randomly editing out a minute of film from two movies and swapping them. Perhaps the fifth minute of Bambi is swapped for the fifth minute of a Shrek film. Clearly, the closer that two frames of film are together, the more likely they are to move or remain together. 3. In some ways, sex-linked genes reflect the risk of not having a backup copy of a file on your computer. If you only have one copy and it is damaged, you have to live with the damaged file. Having two X chromosomes in females provides a “backup copy” that can function if one of the sex-linked genes is damaged. 4. Hemophilia and other genetic diseases may also result from spontaneous mutations in a family with no known history of the disease. Although rare, this possibility should always be considered when tracing the history of an inherited disease. 5. Female hemophiliacs are very rare because both X chromosomes would need to have the recessive trait. Although very unlikely, female hemophiliacs are known. Students may enjoy searching for details of these rare cases. For additional information about hemophilia, consider visiting the website of the National Hemophilia Foundation at www.hemophilia.org. Active Lecture Tips 1. See the activity Pairs of Shoes and Pairs of Chromosomes on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 2. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 124

Sex-Linked Genes Red-green colorblindness is a common sex-linked disorder caused by a malfunction of light-sensitive cells in the eyes. Mostly males are affected, but heterozygous females have some defects, too. Figure 9.26 shows a simple test for red-green colorblindness. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. This section of the chapter relies on a good understanding of the chromosome sorting process of meiosis. If students were not assigned Chapter 8, and meiosis was not otherwise addressed, it will be difficult for students to understand the chromosomal basis of inheritance or linked genes. 2. The nature of linked genes builds on our natural expectations that items that are closer together are less likely to be separated. Yet students may find such concepts initially foreign. Whether it is parents holding the hands of children or people and their pets, we generally know that separation is more likely when things are farther apart. You might demonstrate this simply by drawing a line down a page of text. The likelihood that the line separates any pair of words increases, as the distance between the words grows farther apart. 3. The discussion of “linked genes” addresses a different relationship than the use of the similar termed “sex-linked genes.” The nature of the linkage is quite different. Consider emphasizing this distinction for your students. 4. The likelihood that at least some students are colorblind in larger classes is very high. Some of these students might find this interesting and want to discuss it further. However, others might be embarrassed by what might be perceived as a defect. Teaching Tips 1. Building on the shoe analogy developed in Chapter 8, linked genes are like a shoe and its shoelaces. The two are usually transferred together but can be moved separately under special circumstances. 2. Crossing over (from Chapter 8) is like randomly editing out a minute of film from two movies and swapping them. Perhaps the fifth minute of Bambi is swapped for the fifth minute of a Shrek film. Clearly, the closer that two frames of film are together, the more likely they are to move or remain together. 3. In some ways, sex-linked genes reflect the risk of not having a backup copy of a file on your computer. If you only have one copy and it is damaged, you have to live with the damaged file. Having two X chromosomes in females provides a “backup copy” that can function if one of the sex-linked genes is damaged. 4. Hemophilia and other genetic diseases may also result from spontaneous mutations in a family with no known history of the disease. Although rare, this possibility should always be considered when tracing the history of an inherited disease. 5. Female hemophiliacs are very rare because both X chromosomes would need to have the recessive trait. Although very unlikely, female hemophiliacs are known. Students may enjoy searching for details of these rare cases. For additional information about hemophilia, consider visiting the website of the National Hemophilia Foundation at www.hemophilia.org. Active Lecture Tips 1. See the activity Pairs of Shoes and Pairs of Chromosomes on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 2. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 125

Figure 9.26 Figure 9.26 A test for red-green colorblindness

Sex-Linked Genes Because they are located on the sex chromosomes, sex-linked genes exhibit unusual inheritance patterns. Figure 9.27a illustrates what happens when a colorblind male has offspring with a homozygous female with normal color vision. Figure 9.27b illustrates what happens if a female carrier mates with a male who has normal color vision. Because the colorblindness allele is recessive, a female will be colorblind only if she receives that allele on both X chromosomes. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. This section of the chapter relies on a good understanding of the chromosome sorting process of meiosis. If students were not assigned Chapter 8, and meiosis was not otherwise addressed, it will be difficult for students to understand the chromosomal basis of inheritance or linked genes. 2. The nature of linked genes builds on our natural expectations that items that are closer together are less likely to be separated. Yet students may find such concepts initially foreign. Whether it is parents holding the hands of children or people and their pets, we generally know that separation is more likely when things are farther apart. You might demonstrate this simply by drawing a line down a page of text. The likelihood that the line separates any pair of words increases, as the distance between the words grows farther apart. 3. The discussion of “linked genes” addresses a different relationship than the use of the similar termed “sex-linked genes.” The nature of the linkage is quite different. Consider emphasizing this distinction for your students. 4. The likelihood that at least some students are colorblind in larger classes is very high. Some of these students might find this interesting and want to discuss it further. However, others might be embarrassed by what might be perceived as a defect. Teaching Tips 1. Building on the shoe analogy developed in Chapter 8, linked genes are like a shoe and its shoelaces. The two are usually transferred together but can be moved separately under special circumstances. 2. Crossing over (from Chapter 8) is like randomly editing out a minute of film from two movies and swapping them. Perhaps the fifth minute of Bambi is swapped for the fifth minute of a Shrek film. Clearly, the closer that two frames of film are together, the more likely they are to move or remain together. 3. In some ways, sex-linked genes reflect the risk of not having a backup copy of a file on your computer. If you only have one copy and it is damaged, you have to live with the damaged file. Having two X chromosomes in females provides a “backup copy” that can function if one of the sex-linked genes is damaged. 4. Hemophilia and other genetic diseases may also result from spontaneous mutations in a family with no known history of the disease. Although rare, this possibility should always be considered when tracing the history of an inherited disease. 5. Female hemophiliacs are very rare because both X chromosomes would need to have the recessive trait. Although very unlikely, female hemophiliacs are known. Students may enjoy searching for details of these rare cases. For additional information about hemophilia, consider visiting the website of the National Hemophilia Foundation at www.hemophilia.org. Active Lecture Tips 1. See the activity Pairs of Shoes and Pairs of Chromosomes on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 2. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 127

(a) Normal female  colorblind male (b) Carrier female  normal male Figure 9.27 XNXN XnY XNXn XNY Xn Y Sperm XN Y Sperm Eggs XN XNXn XNY Eggs XN XNXN XNY XN XNXn XNY Xn XNXn XnY (a) Normal female  colorblind male (b) Carrier female  normal male XNXn XnY Key Xn Y Sperm Unaffected individual Carrier Eggs XN XNXn XNY Colorblind individual Xn XnXn XnY (c) Carrier female  colorblind male Figure 9.27 Inheritance of colorblindness, a sex-linked recessive trait

(a) Normal female  colorblind male Figure 9.27-1 XNXN XnY Key Unaffected individual Xn Y Sperm Carrier Eggs XN XNXn XNY Colorblind individual XN XNXn XNY (a) Normal female  colorblind male Figure 9.27-1 Inheritance of colorblindness, a sex-linked recessive trait (part 1: normal female and colorblind male)

(b) Carrier female  normal male Figure 9.27-2 XNXn XNY Key Unaffected individual XN Y Sperm Carrier Eggs XN XNXN XNY Colorblind individual Xn XNXn XnY (b) Carrier female  normal male Figure 9.27-2 Inheritance of colorblindness, a sex-linked recessive trait (part 2: carrier female and normal male)

(c) Carrier female  colorblind male Figure 9.27-3 XNXn XnY Key Xn Y Unaffected individual Sperm Carrier Eggs XN XNXn XNY Colorblind individual Xn XnXn XnY (c) Carrier female  colorblind male Figure 9.27-3 Inheritance of colorblindness, a sex-linked recessive trait (part 3: carrier female and colorblind male)

Sex-Linked Genes Hemophilia is a sex-linked recessive trait with a long, well-documented history. Hemophiliacs bleed excessively when injured because they have inherited an abnormal allele for a factor involved in blood clotting. The most seriously affected individuals may bleed to death after relatively minor bruises or cuts. The age-old practice of strengthening international alliances by marriage effectively spread hemophilia through the royal families of several nations. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. This section of the chapter relies on a good understanding of the chromosome sorting process of meiosis. If students were not assigned Chapter 8, and meiosis was not otherwise addressed, it will be difficult for students to understand the chromosomal basis of inheritance or linked genes. 2. The nature of linked genes builds on our natural expectations that items that are closer together are less likely to be separated. Yet students may find such concepts initially foreign. Whether it is parents holding the hands of children or people and their pets, we generally know that separation is more likely when things are farther apart. You might demonstrate this simply by drawing a line down a page of text. The likelihood that the line separates any pair of words increases, as the distance between the words grows farther apart. 3. The discussion of “linked genes” addresses a different relationship than the use of the similar termed “sex-linked genes.” The nature of the linkage is quite different. Consider emphasizing this distinction for your students. 4. The likelihood that at least some students are colorblind in larger classes is very high. Some of these students might find this interesting and want to discuss it further. However, others might be embarrassed by what might be perceived as a defect. Teaching Tips 1. Building on the shoe analogy developed in Chapter 8, linked genes are like a shoe and its shoelaces. The two are usually transferred together but can be moved separately under special circumstances. 2. Crossing over (from Chapter 8) is like randomly editing out a minute of film from two movies and swapping them. Perhaps the fifth minute of Bambi is swapped for the fifth minute of a Shrek film. Clearly, the closer that two frames of film are together, the more likely they are to move or remain together. 3. In some ways, sex-linked genes reflect the risk of not having a backup copy of a file on your computer. If you only have one copy and it is damaged, you have to live with the damaged file. Having two X chromosomes in females provides a “backup copy” that can function if one of the sex-linked genes is damaged. 4. Hemophilia and other genetic diseases may also result from spontaneous mutations in a family with no known history of the disease. Although rare, this possibility should always be considered when tracing the history of an inherited disease. 5. Female hemophiliacs are very rare because both X chromosomes would need to have the recessive trait. Although very unlikely, female hemophiliacs are known. Students may enjoy searching for details of these rare cases. For additional information about hemophilia, consider visiting the website of the National Hemophilia Foundation at www.hemophilia.org. Active Lecture Tips 1. See the activity Pairs of Shoes and Pairs of Chromosomes on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 2. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 132

Queen Victoria Albert Alice Louis Alexandra Czar Nicholas II of Russia Figure 9.28 Queen Victoria Albert Alice Louis Alexandra Czar Nicholas II of Russia Alexis Figure 9.28 Hemophilia in the royal family of Russia

Queen Albert Victoria Alice Louis Alexandra Czar Nicholas II of Russia Figure 9.28-1 Queen Victoria Albert Alice Louis Alexandra Czar Nicholas II of Russia Alexis Figure 9.28-1 Hemophilia in the royal family of Russia (part 1: pedigree)

Figure 9.28-2 Figure 9.28-2 Hemophilia in the royal family of Russia (part 2: photo)

Evolution Connection: Barking Up the Evolutionary Tree About 15,000 years ago, in East Asia, people began to cohabit with ancestral canines that were predecessors of both modern wolves and dogs. As people moved into permanent, geographically isolated settlements, populations of canines were separated from one another and eventually became inbred. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. This section of the chapter relies on a good understanding of the chromosome sorting process of meiosis. If students were not assigned Chapter 8, and meiosis was not otherwise addressed, it will be difficult for students to understand the chromosomal basis of inheritance or linked genes. 2. The nature of linked genes builds on our natural expectations that items that are closer together are less likely to be separated. Yet students may find such concepts initially foreign. Whether it is parents holding the hands of children or people and their pets, we generally know that separation is more likely when things are farther apart. You might demonstrate this simply by drawing a line down a page of text. The likelihood that the line separates any pair of words increases, as the distance between the words grows farther apart. 3. The discussion of “linked genes” addresses a different relationship than the use of the similar termed “sex-linked genes.” The nature of the linkage is quite different. Consider emphasizing this distinction for your students. 4. The likelihood that at least some students are colorblind in larger classes is very high. Some of these students might find this interesting and want to discuss it further. However, others might be embarrassed by what might be perceived as a defect. Teaching Tips 1. Building on the shoe analogy developed in Chapter 8, linked genes are like a shoe and its shoelaces. The two are usually transferred together but can be moved separately under special circumstances. 2. Crossing over (from Chapter 8) is like randomly editing out a minute of film from two movies and swapping them. Perhaps the fifth minute of Bambi is swapped for the fifth minute of a Shrek film. Clearly, the closer that two frames of film are together, the more likely they are to move or remain together. 3. In some ways, sex-linked genes reflect the risk of not having a backup copy of a file on your computer. If you only have one copy and it is damaged, you have to live with the damaged file. Having two X chromosomes in females provides a “backup copy” that can function if one of the sex-linked genes is damaged. 4. Hemophilia and other genetic diseases may also result from spontaneous mutations in a family with no known history of the disease. Although rare, this possibility should always be considered when tracing the history of an inherited disease. 5. Female hemophiliacs are very rare because both X chromosomes would need to have the recessive trait. Although very unlikely, female hemophiliacs are known. Students may enjoy searching for details of these rare cases. For additional information about hemophilia, consider visiting the website of the National Hemophilia Foundation at www.hemophilia.org. Active Lecture Tips 1. See the activity Pairs of Shoes and Pairs of Chromosomes on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 2. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 136

Evolution Connection: Barking Up the Evolutionary Tree A 2010 study indicated that small dogs were first bred within early agricultural settlements of the Middle East around 12,000 years ago. Continued over millennia, such genetic tinkering has resulted in a diverse array of dog body types and behaviors. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. This section of the chapter relies on a good understanding of the chromosome sorting process of meiosis. If students were not assigned Chapter 8, and meiosis was not otherwise addressed, it will be difficult for students to understand the chromosomal basis of inheritance or linked genes. 2. The nature of linked genes builds on our natural expectations that items that are closer together are less likely to be separated. Yet students may find such concepts initially foreign. Whether it is parents holding the hands of children or people and their pets, we generally know that separation is more likely when things are farther apart. You might demonstrate this simply by drawing a line down a page of text. The likelihood that the line separates any pair of words increases, as the distance between the words grows farther apart. 3. The discussion of “linked genes” addresses a different relationship than the use of the similar termed “sex-linked genes.” The nature of the linkage is quite different. Consider emphasizing this distinction for your students. 4. The likelihood that at least some students are colorblind in larger classes is very high. Some of these students might find this interesting and want to discuss it further. However, others might be embarrassed by what might be perceived as a defect. Teaching Tips 1. Building on the shoe analogy developed in Chapter 8, linked genes are like a shoe and its shoelaces. The two are usually transferred together but can be moved separately under special circumstances. 2. Crossing over (from Chapter 8) is like randomly editing out a minute of film from two movies and swapping them. Perhaps the fifth minute of Bambi is swapped for the fifth minute of a Shrek film. Clearly, the closer that two frames of film are together, the more likely they are to move or remain together. 3. In some ways, sex-linked genes reflect the risk of not having a backup copy of a file on your computer. If you only have one copy and it is damaged, you have to live with the damaged file. Having two X chromosomes in females provides a “backup copy” that can function if one of the sex-linked genes is damaged. 4. Hemophilia and other genetic diseases may also result from spontaneous mutations in a family with no known history of the disease. Although rare, this possibility should always be considered when tracing the history of an inherited disease. 5. Female hemophiliacs are very rare because both X chromosomes would need to have the recessive trait. Although very unlikely, female hemophiliacs are known. Students may enjoy searching for details of these rare cases. For additional information about hemophilia, consider visiting the website of the National Hemophilia Foundation at www.hemophilia.org. Active Lecture Tips 1. See the activity Pairs of Shoes and Pairs of Chromosomes on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 2. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 137

Evolution Connection: Barking Up the Evolutionary Tree Our understanding of canine evolution took a big leap forward when researchers sequenced the complete genome of a dog. Using the genome sequence and a wealth of other data, canine geneticists produced an evolutionary tree based on a genetic analysis of 85 breeds. The formulation of an evolutionary tree for the domestic dog shows that new technologies can provide important insights into genetic and evolutionary questions about life on Earth. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. This section of the chapter relies on a good understanding of the chromosome sorting process of meiosis. If students were not assigned Chapter 8, and meiosis was not otherwise addressed, it will be difficult for students to understand the chromosomal basis of inheritance or linked genes. 2. The nature of linked genes builds on our natural expectations that items that are closer together are less likely to be separated. Yet students may find such concepts initially foreign. Whether it is parents holding the hands of children or people and their pets, we generally know that separation is more likely when things are farther apart. You might demonstrate this simply by drawing a line down a page of text. The likelihood that the line separates any pair of words increases, as the distance between the words grows farther apart. 3. The discussion of “linked genes” addresses a different relationship than the use of the similar termed “sex-linked genes.” The nature of the linkage is quite different. Consider emphasizing this distinction for your students. 4. The likelihood that at least some students are colorblind in larger classes is very high. Some of these students might find this interesting and want to discuss it further. However, others might be embarrassed by what might be perceived as a defect. Teaching Tips 1. Building on the shoe analogy developed in Chapter 8, linked genes are like a shoe and its shoelaces. The two are usually transferred together but can be moved separately under special circumstances. 2. Crossing over (from Chapter 8) is like randomly editing out a minute of film from two movies and swapping them. Perhaps the fifth minute of Bambi is swapped for the fifth minute of a Shrek film. Clearly, the closer that two frames of film are together, the more likely they are to move or remain together. 3. In some ways, sex-linked genes reflect the risk of not having a backup copy of a file on your computer. If you only have one copy and it is damaged, you have to live with the damaged file. Having two X chromosomes in females provides a “backup copy” that can function if one of the sex-linked genes is damaged. 4. Hemophilia and other genetic diseases may also result from spontaneous mutations in a family with no known history of the disease. Although rare, this possibility should always be considered when tracing the history of an inherited disease. 5. Female hemophiliacs are very rare because both X chromosomes would need to have the recessive trait. Although very unlikely, female hemophiliacs are known. Students may enjoy searching for details of these rare cases. For additional information about hemophilia, consider visiting the website of the National Hemophilia Foundation at www.hemophilia.org. Active Lecture Tips 1. See the activity Pairs of Shoes and Pairs of Chromosomes on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 2. See the Media Review: “Learn.Genetics” Genetic Science Learning Center from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 138

Wolf Chinese shar-pei Ancestral canine Akita Basenji Figure 9.29 Wolf Chinese shar-pei Ancestral canine Siberian husky Akita Alaskan malamute Basenji Afghan hound Saluki Rottweiler Sheepdog Retriever Figure 9.29 An evolutionary tree of dog breeds

Figure 9.29-1 Figure 9.29-1 An evolutionary tree of dog breeds (part 1: photo)

(allele pairs separated) Figure 9.UN01 Fertilization Alleles Meiosis Gamete from other parent Diploid zygote (contains paired alleles) Diploid cell (contains paired alleles, alternate forms of a gene) Haploid gametes (allele pairs separated) Figure 9.UN01 Summary of key concepts: law of segregation

Dominant P ? Recessive pp Figure 9.UN02 Phenotype Dominant P ? Recessive pp Genotype or Phenotype All dominant 1 dominant:1 recessive Conclusion Unknown parent is PP Unknown parent is Pp Figure 9.UN02 Summary of key concepts: testcross

Intermediate phenotype (incomplete dominance) Figure 9.UN03 Dominant phenotype (RR) Recessive phenotype (rr) Intermediate phenotype (incomplete dominance) (Rr) Figure 9.UN03 Summary of key concepts: incomplete dominance

Multiple traits Pleiotropy (e.g., sickle-cell Single disease) gene Figure 9.UN04 Pleiotropy Multiple traits (e.g., sickle-cell disease) Single gene Figure 9.UN04 Summary of key concepts: pleiotropy

Polygenic inheritance Single trait (e.g., height) Multiple genes Figure 9.UN05 Polygenic inheritance Single trait (e.g., height) Multiple genes Figure 9.UN05 Summary of key concepts: polygenic inheritance

Male Female 44 + XY 44 + XX Somatic cells Figure 9.UN06 Figure 9.UN06 Summary of key concepts: sex determination

Figure 9.UN07 Figure 9.UN07 Summary of key concepts: sex-linked traits

Figure 9.UN08 Figure 9.UN08 Process of science, question 18 (“curl” cat)

Parents Hearing Dd Hearing Dd Offspring D d Sperm Dd Hearing (carrier) Figure 9.UN09 Parents Hearing Dd Hearing Dd Offspring D d Sperm Dd Hearing (carrier) DD Hearing D Eggs Dd Hearing (carrier) dd Deaf d Figure 9.UN09 Process of science, question 19 (Punnett square for deafness)

Figure 9.UN10 Figure 9.UN10 Process of science, question 20 (Cavalier King Charles dog)