1. Patterns of Inheritance

2. The science of genetics has ancient roots
(400 BCE) An early explanation for inheritance suggested that particles called pangenes came from all parts of the organism and were incorporated into eggs or sperm to be passed to offspring.
(1800s)The idea that hereditary materials mix in forming offspring, called the blending hypothesis, was suggested but later rejected because it did not explain how traits that disappear in one generation can reappear in later generations.
Teaching Tips
1. As you begin your lectures on genetics, consider challenging your students to explain why the theories of pangenesis and blending are incorrect. Perhaps just pick one of the two. You might even ask for short responses from everyone at the start of class or as an assignment before the first lectures. In addition to arousing interest in the answers, the responses should reveal the diverse backgrounds of your students entering this discussion and reveal any preexisting confusion on the subject of genetics.
2. The concept of pangenesis is analogous to the structure of United States representation in Congress. Each congressional district sends a congressman or congresswoman (pangene) to the U.S. House of Representatives (gamete). There, all parts of the United States (body) are represented.
3. In this or future lectures addressing evolution, you may mention that pangenesis was a mechanism consistent with Lamarckian evolution. 2

3. Experimental genetics began in an abbey garden (mid 1800s)
Heredity is the transmission of traits from one generation to the next.
Genetics is the scientific study of heredity.
Gregor Mendel (1860s)
Father of modern genetics
Experimented with garden peas
Found patterns to inheritance of traits
Inheritance could be predicted
Student Misconceptions and Concerns
The authors note that Mendel’s work was published in 1866, seven years after Darwin published Origin of Species. Consider challenging your students to consider whether Mendel’s findings supported 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, rather than the possibility for such gradual inheritance.
Teaching Tips
1. In Module 9.2, the authors make the analogy between genes and playing cards, noting that each are shuffled but retain their original identity. This analogy may form a very useful reference point for your students and can be used later, as new principles of genetics are discussed.
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

4. Experimental genetics began in an abbey garden
Mendel used pea plants. Why are they a good organism for genetic studies? Mendel found evidence to support that – parents pass on to their offspring discrete “heritable factors” and – the heritable factors (today called genes), retain their individuality generation after generation.
Student Misconceptions and Concerns
The authors note that Mendel’s work was published in 1866, seven years after Darwin published Origin of Species. Consider challenging your students to consider whether Mendel’s findings supported 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, rather than the possibility for such gradual inheritance.
Teaching Tips
1. In Module 9.2, the authors make the analogy between genes and playing cards, noting that each are shuffled but retain their original identity. This analogy may form a very useful reference point for your students and can be used later, as new principles of genetics are discussed.
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. 4

6. Parents (P) Offspring (F1)
White 1
Removal of stamens
Stamens
Carpel 2
Transfer of pollen
Parents (P)
Purple 3
Carpel matures into pea pod 4
Seeds from pod planted
Figure 9.2C_s3 Mendel’s technique for cross-fertilization of pea plants (step 3)
Offspring (F1) 6

7. Experimental genetics began in an abbey garden
True-breeding varieties result when self-fertilization produces offspring all identical to the parent.
The offspring of two different varieties are hybrids.
The cross-fertilization is a hybridization, or genetic cross.
Parental plants are the P generation.
Offspring/Filial = F1 generation.
A cross of F1 plants produces an F2 generation.
Student Misconceptions and Concerns
The authors note that Mendel’s work was published in 1866, seven years after Darwin published Origin of Species. Consider challenging your students to consider whether Mendel’s findings supported 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, rather than the possibility for such gradual inheritance.
Teaching Tips
1. In Module 9.2, the authors make the analogy between genes and playing cards, noting that each are shuffled but retain their original identity. This analogy may form a very useful reference point for your students and can be used later, as new principles of genetics are discussed.
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. 7

8. Genetics Vocabulary
Gene-segment of DNA that had the coding for a particular trait.
Allele- one of several varieties of a gene.
Locus- location on a chromosome where the gene is located
Testcross-mating between an individual of unknown genotype and a known(homozygous recessive individual)
… dominant, recessive, homozygous, heterozygous, phenotype, genotype
Student Misconceptions and Concerns
Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. We would expect that any six playing cards dealt might be half black and half red, but 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 will reflect expected ratios.
Teaching Tips
Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. (If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three dark and one brown or all dark. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype.) 8

9. of plants have purple flowers of plants have white flowers
The Experiment
P generation (true-breeding parents) 
Purple flowers
White flowers
F1 generation
All plants have purple flowers
Fertilization among F1 plants (F1  F1)
Figure 9.3A_s3 Crosses tracking one character (flower color) (step 3)
F2 generation
of plants have purple flowers 3 4
of plants have white flowers 1 4 9

10. The seven pea characteristics studied by Mendel
Traits
Dominant
Recessive
Flower color
The seven pea characteristics
studied by Mendel
Purple
White
Flower position
Axial
Terminal
Seed color
Yellow
Green
Seed shape
Round
Wrinkled
Pod shape
Inflated
Constricted
Figure 9.2D The seven pea characters studied by Mendel
Pod color
Green
Yellow
Stem length
Tall
Dwarf 10

11. Mendel’s Discoveries Principle of Dominance
Law (Principle) of Segregation
Law (Principle) of Independent Assortment

12. Mendel’s Theory of Segregation
An individual inherits a unit of information (allele) about a trait from each parent
During gamete formation, the alleles segregate from each other (homologous chromosomes separate from each other, one allele of each gene from each parent is passed to offspring)

13. Alleles
Different molecular forms of a gene
Arise by mutation

14. Homologous chromosomes bear the alleles for each character
A locus (plural, loci) is the specific location of a gene along a chromosome.
For a pair of homologous chromosomes, alleles of a gene reside at the same locus.
Student Misconceptions and Concerns
Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. We would expect that any six playing cards dealt might be half black and half red, but 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 will reflect expected ratios.
Teaching Tips
Figure 9.4 can be of great benefit when introducing genetic terminology. For students struggling to think abstractly, such a visual aid may be essential when describing these features in lecture. 14

15. The law of independent assortment is revealed by tracking two characters at once
A dihybrid cross is a mating of parental varieties that differ in two characters.
Mendel performed the following dihybrid cross with the following results:
P generation: round yellow seeds  wrinkled green seeds
F1 generation: all plants with round yellow seeds
F2 generation:
9/16 had round yellow seeds
3/16 had wrinkled yellow seeds
3/16 had round green seeds
1/16 had wrinkled green seeds
Student Misconceptions and Concerns
Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. We would expect that any six playing cards dealt might be half black and half red, but 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 will reflect expected ratios.
Teaching Tips
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 occurring simultaneously. 15

16. F1 generation RrYy Sperm RY Ry rY ry RY RRYY RrYY RRYy RrYy rY4 1 RY 4 1 4 1 Ry 4 1 rY ry 4 1 RY
RRYY
RrYY
RRYy
RrYy 4 1 rY 16 9
Yellow round
RrYY
rrYY
RrYy
rrYy
Eggs 16 3 4 1
Green round Ry
Figure 9.5A_3 Two hypotheses for segregation in a dihybrid cross (part 3)
RRYy
RrYy
RRyy
Rryy 16 3
Yellow wrinkled 4 1 ry 16 1
Green wrinkled
RrYy
rrYy
Rryy
rryy
The hypothesis of independent assortment Actual results; hypothesis supported 16

17. All yellow round seeds (RrYy) Meta- phase I of meiosis
F1 generation
All yellow round seeds (RrYy) R y r Y R r r R
Meta- phase I of meiosis Y y Y y R r r R
Anaphase I Y y Y y
Metaphase II R r r R Y y Y y
Gametes
Figure 9.16_s3 The chromosomal basis of Mendel’s laws (step 3) y Y Y y Y Y y y R R r r r r R R 4 1 4 1 4 1 4 1 RY ry rY Ry
Fertilization
F2 generation 9 :3 :3 :1 17

18. Mendel’s Law of Independent Assortment
Mendel concluded that the two “units” for a trait were to be assorted into gametes independently of any other “units” for the other traits
Members of each pair of homologous chromosomes are sorted into gametes at random during meiosis
1/4 AB
1/4 ab
1/4 Ab
1/4 aB
Allelic combinations
possible in gametes

19. Genetics is more complicated than Mendel’s experiments lead him to understand….

20. Dominance Relationships:
Inheritance Patterns
Dominance Relationships:
Complete dominance (Simple dominance)
Incomplete dominance
Codominance
Multiple Alleles
X-linked
Gene Interactions:
- Pleiotrophy
- Polygenic

21. Incomplete Dominance- Incomplete Dominance X Homozygous parent
Example snapdragons
Incomplete Dominance X
Homozygous
parent
Homozygous
parent
All F1 are
heterozygous
Another example of incomplete dominance in humans is hypercholesterolemia, dangerously high levels of cholesterol occur in the blood - heterozygotes have intermediately high cholesterol levels. X
F2 shows three phenotypes in 1:2:1 ratio

22. Many genes have more than two alleles in the population (multiple alleles) Human ABO blood group phenotypes involve three alleles for a single gene.
Blood Group (Phenotype)
Antibodies Present in Blood
Reaction When Blood from Groups Below Is Mixed with Antibodies from Groups at Left
Carbohydrates Present on Red Blood Cells
Genotypes O A B AB
IAIA or IAi
Carbohydrate A A
Anti-B
IBIB or IBi
Carbohydrate B B
Anti-A
Carbohydrate A and Carbohydrate B AB
IAIB
None
Figure 9.12 Multiple alleles for the ABO blood groups
Anti-A O ii
Neither
Anti-B
No reaction
Clumping reaction 22

23. Chromosomes determine sex in many species
Many animals have a pair of sex chromosomes,
designated X and Y,
that determine an individual’s sex.
In mammals,
males have XY sex chromosomes,
females have XX sex chromosomes,
the Y chromosome has the SRY gene for the development of testes, and
an absence of the Y allows ovaries to develop.
Teaching Tips
As the text notes, in crocodilians and many turtles, sex is not genetically determined. Instead, the incubation temperature of the eggs determines an animal’s sex. Students may enjoy researching this unique form of sex determination, often identified as TSD (temperature-dependent sex determination). 23

24. Chromosomes determine sex in many species
Some organisms lack sex chromosomes altogether.
In bees, sex is determined by chromosome number.
Females are diploid.
Males are haploid.
In some species sex is determined by the temperature at which the eggs are incubated. (some crocodiles and turtles)
Teaching Tips
As the text notes, in crocodilians and many turtles, sex is not genetically determined. Instead, the incubation temperature of the eggs determines an animal’s sex. Students may enjoy researching this unique form of sex determination, often identified as TSD (temperature-dependent sex determination). 24

25. Sex-linked genes exhibit a unique pattern of inheritance
Sex-linked genes are located on either of the sex chromosomes.
The X chromosome carries many genes unrelated to sex. These genes are called X-linked.
Ex- The inheritance of white eye color in the fruit fly illustrates an X-linked recessive trait.
Student Misconceptions and Concerns
The prior discussion of linked genes addresses a different relationship than the use of the similar term sex-linked genes. Consider emphasizing this distinction for your students.
Teaching Tips
An analogy can be drawn between sex-linked genes and 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. Females, who have two X chromosomes, thus have a “backup copy” that can function if one of the sex-linked genes is damaged. 25

26. Sex-linked traits
Examples- red-green colorblindness, Hemophilia, Duchenne’s muscular dystrophy
Cross a colorblind male with a female that is a carrier for the trait.
_______x _______
hemophilia, characterized by excessive bleeding because hemophiliacs lack one or more of the proteins required for blood clotting,
red-green color blindness, a malfunction of light-sensitive cells in the eyes, and
Duchenne muscular dystrophy, a condition characterized by a progressive weakening of the muscles and loss of coordination.

27. X- Inactiviation

28. Nondisjunction

29. A single character may be influenced by many genes
Many characteristics result from polygenic inheritance, in which a single phenotypic character results from the additive effects of two or more genes.
Student Misconceptions and Concerns
1. After reading the preceding modules, students might expect all traits to be governed by a single gene with two alleles, one dominant over the other. Modules 9.11–9.15 describe deviations from simplistic models of inheritance.
2. 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).
3. 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. 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.
2. 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. 29

30. A single gene may affect many phenotypic characters
Pleiotropy occurs when one gene influences many characteristics.
Sickle-cell disease is a human example of pleiotropy. This disease
affects the type of hemoglobin produced and the shape of red blood cells and
causes anemia and organ damage.
Sickle-cell and nonsickle alleles are codominant.
Carriers of sickle-cell disease are resistant to malaria.
Student Misconceptions and Concerns
1. After reading the preceding modules, students might expect all traits to be governed by a single gene with two alleles, one dominant over the other. Modules 9.11–9.15 describe deviations from simplistic models of inheritance.
2. 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).
3. 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
The American Sickle Cell Anemia Association’s website, is a good place to find additional details. 30

31. Non-Nuclear Inheritance

32. The environment affects many characters
Many characters result from a combination of heredity and the environment. For example,
skin color is affected by exposure to sunlight,
susceptibility to diseases, such as cancer, has hereditary and environmental components, and
identical twins show some differences.
Only genetic influences are inherited.
Nature v. Nuture ( Genes v. Environment)
Student Misconceptions and Concerns
1. After reading the preceding modules, students might expect all traits to be governed by a single gene with two alleles, one dominant over the other. Modules 9.11–9.15 describe deviations from simplistic models of inheritance.
2. 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).
3. 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. 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.
2. 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 and piercing may also help to distinguish between environmental influences and inheritance. Students with tattoos will not produce children born with tattoos! 32

33. Environmental Effects on Plant Phenotype
Hydrangea macrophylla
Action of gene responsible for floral color is influenced by soil acidity
Flower color ranges from pink
to blue

34. Environmental Effects on Plant Phenotype (Yarrow, Achillea millefolium)

35. Temperature Effects on Phenotype
Rabbit is homozygous for an allele that specifies a heat-sensitive version of an enzyme in melanin-producing pathway
Melanin is produced in cooler areas of body

36. Genetic traits in humans can be tracked through family pedigrees
In a simple dominant-recessive inheritance ; one allele is dominant and the other is recessive
P= purple p= white
Cross a heterozygous purple flowering plant with a plant that had white flowers.
Wild-type traits, those prevailing in nature, are not necessarily specified by dominant alleles.
Student Misconceptions and Concerns
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.
Teaching Tips
Students seem to learn much from Figure 9.8b by analyzing the possible genotypes for the people whose complete genotype is not known. Consider challenging your students to suggest the possible genotypes for these people, perhaps during lecture. 36

37. Examples of single-gene inherited traits in humans
Dominant Traits
Recessive Traits
Examples of single-gene inherited traits in humans
Freckles
No freckles
Figure 9.8A Examples of single-gene inherited traits in humans
Widow’s peak
Straight hairline
Free earlobe
Attached earlobe 37

38. Genetic traits in humans can be tracked through family pedigrees
A pedigree
Student Misconceptions and Concerns
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.
Teaching Tips
Students seem to learn much from Figure 9.8b by analyzing the possible genotypes for the people whose complete genotype is not known. Consider challenging your students to suggest the possible genotypes for these people, perhaps during lecture. 38

39. Many inherited disorders in humans are controlled by a single gene
The most common genetic disease in the United States is cystic fibrosis (CF), resulting in excessive thick mucus secretions. The CF allele is
Recessive
Carried by about 1 in 31 Americans.
Shortened life expectancy (40-50 years)
Dominant human disorders include
Achondroplasia, resulting in dwarfism, and
Huntington’s disease, a degenerative disorder of the nervous system.
Teaching Tips
1. The 2/3 fraction noted in the discussion of carriers of a recessive disorder for deafness often catches students off guard as they are expecting odds of 1/4, 1/2, or 3/4. However, when we eliminate the dd (deaf) possibility, as it would not be a carrier, we have three possible genotypes. Thus, the odds are based out of the remaining three genotypes Dd, dD, and DD. Consider adding this point of clarification to your lecture.
2. As a simple test of comprehension, ask students 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. Ask your class a) what the odds are of a person developing Huntington’s disease if a parent has this disease (50%) and b) whether they would want this genetic test if they were a person at risk. The Huntington Disease Society website, offers many additional details. It is a good starting point for those who want to explore this disease in more detail. 39

40. Table 9.9 Some Autosomal Disorders in Humans40

41. New technologies can provide insight into one’s genetic legacy
New technologies offer ways to obtain genetic information
before conception,
during pregnancy, and
after birth.
Genetic testing can identify potential parents who are heterozygous carriers for certain diseases.
Teaching Tips
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 health 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? 41

42. New technologies can provide insight into THE OFFSPRING’s genetic legacy
Several technologies can be used for detecting genetic conditions in a fetus.
Amniocentesis extracts samples of amniotic fluid containing fetal cells and permits
karyotyping and
biochemical tests on cultured fetal cells to detect other conditions, such as Tay-Sachs disease.
Chorionic villus sampling removes a sample of chorionic villus tissue from the placenta and permits similar karyotyping and biochemical tests.
Teaching Tips
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 health 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? 42

43. Chorionic Villus Sampling (CVS)
Amniocentesis
Chorionic Villus Sampling (CVS)
Amniotic fluid extracted
Tissue extracted from the chorionic villi
Ultrasound transducer
Ultrasound transducer
Fetus
Fetus
Placenta
Placenta
Uterus
Chorionic villi
Cervix
Cervix
Uterus
Centrifugation
Amniotic fluid
Biochemical and genetics tests
Fetal cells
Fetal cells
Several hours
Several hours
Figure 9.10A Testing a fetus for genetic disorders
Cultured cells
Several weeks
Several weeks
Several hours
Karyotyping 43

44. New technologies can provide insight into THE OFFSPRING’s genetic legacy
Blood tests on the mother at 14–20 weeks of pregnancy can help identify fetuses at risk for certain birth defects.
Fetal imaging, the most common procedure is ultrasound imaging, uses sound waves to produce a picture of the fetus.
Newborn screening can detect diseases that can be prevented by special care and precautions.
Teaching Tips
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 health 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? 44

45. Figure 9.10B Ultrasound scanning of a fetus45

46. New technologies can provide insight into one’s genetic legacy
New technologies raise ethical considerations that include
the confidentiality and potential use of results of genetic testing,
time and financial costs, and
determining what, if anything, should be done as a result of the testing.
Teaching Tips
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 health 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? 46

47. Genes on the same chromosome tend to be inherited together
Linked genes, which
are located close together on the same chromosome and
tend to be inherited together.
Student Misconceptions and Concerns
This section of the chapter relies upon a good understanding of the chromosome-sorting process of meiosis. If students were not assigned Chapter 8, and meiosis has not otherwise been addressed, it will be difficult for students to understand the chromosomal basis of inheritance or linked genes.
Teaching Tips
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. 47

48. Crossing over produces new combinations of alleles
Crossing over between homologous chromosomes produces new combinations of alleles in gametes / new chromosomes!.
Student Misconceptions and Concerns
1. This section of the chapter relies upon a good understanding of the chromosome-sorting process of meiosis. If students were not assigned Chapter 8, and meiosis has not otherwise been addressed, it will be difficult for students to understand the chromosomal basis of inheritance or linked genes.
2. The nature of linked genes builds upon our natural expectations that items that are closely 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.
Teaching Tips
1. 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 Avatar. Clearly, the closer together two frames of film are, the more likely they are to move or remain together.
2. Challenge students to explain why Sturtevant and Morgan studied the genetics of fruit flies. As the text notes, their small size, ease of care, and ability to produce several generations in a matter of weeks or months were important factors. 48

49. Geneticists use crossover data to map genes
When examining recombinant frequency (crossing over), the greater the distance between two genes on a chromosome, the more points there are between them where crossing over can occur.
Recombination frequencies can thus be used to map the relative position of genes on chromosomes.
Student Misconceptions and Concerns
1. This section of the chapter relies upon a good understanding of the chromosome-sorting process of meiosis. If students were not assigned Chapter 8, and meiosis has not otherwise been addressed, it will be difficult for students to understand the chromosomal basis of inheritance or linked genes.
2. The nature of linked genes builds upon our natural expectations that items that are closely 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.
Teaching Tips
1. 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 Avatar. Clearly, the closer together two frames of film are, the more likely they are to move or remain together.
2. Challenge students to explain why Sturtevant and Morgan studied the genetics of fruit flies. As the text notes, their small size, ease of care, and ability to produce several generations in a matter of weeks or months were important factors. 49

51. Czar Nicholas II of Russia
Queen Victoria
Albert
Alice
Louis
Female
Male
Alexandra
Czar Nicholas II of Russia
Hemophilia
Figure 9.22 Hemophilia in the royal family of Russia
Carrier
Normal
Alexis 51

52. Most compounds are synthesized by a sequence of metabolic steps involving many enzymes. If the enzymes (proteins) are not present or altered in some way (as in- the instructions coded for in the gene are altered) the compound will be affected.
In addition to simple gene inheritance; environmental factors, interactions between genes, mutations, even nutrition can have an effect on how a gene is expressed. This makes genetics a difficult and complex field of study.

53. You should now be able to
Define and distinguish between these terms: the P generation, the F1 generation, and the F2 generation.
Define and distinguish between the following pairs of terms: homozygous and heterozygous; dominant allele and recessive allele; genotype and phenotype. Also, define a monohybrid cross and a Punnett square. 53

54. You should now be able to
Name and explain Mendel’s laws.
Describe the structure of homologous chromosomes.
Explain how family pedigrees can help determine the inheritance of many human traits.
Explain how recessive and dominant disorders are inherited. (be able to use a Punnett square)
Describe the types and use of fetal testing: amniocentesis, chorionic villus sampling, and ultrasound imaging. 54

55. You should now be able to
Describe the inheritance patterns of incomplete dominance, multiple alleles, codominance, pleiotropy, and polygenic inheritance. Be able to do crossed involving incomplete dominance and ABO blood group. 55

56. You should now be able to
Define the term: linked genes.
Explain how sex is genetically determined in humans and the significance of the SRY gene.
Describe patterns of sex-linked inheritance and examples of sex-linked disorders. Be able to do a Punnett Square. 56