BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Neil A. Campbell Jane B. Reece Lawrence G. Mitchell Martha R. Taylor From PowerPoint ® Lectures for Biology: Concepts & Connections Chapter 14 Mendel and the Gene Idea

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Gregor Mendel is the father of modern genetics. He was an Austrian monk from the 1860s. Gregor Mendel Figure 9.2A, B Stamen Carpel

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Mendel bred pea plants and studied how their traits changed depending on the parent plants. A character is a heritable feature like flower color A trait is a variation of a character (purple or white) Figure 9.2C 1 Removed stamens from purple flower White Stamens Carpel Purple PARENTS (P) OFF- SPRING (F 1 ) 2 Transferred pollen from stamens of white flower to carpel of purple flower 3 Pollinated carpel matured into pod 4 Planted seeds from pod

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Mendel studied seven pea characteristics True-breeding plants make offspring that are the same as the parents every time Figure 9.2D FLOWER COLOR FLOWER POSITION SEED COLOR SEED SHAPE POD SHAPE POD COLOR STEM LENGTH PurpleWhite AxialTerminal YellowGreen RoundWrinkled InflatedConstricted GreenYellow TallDwarf

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings From his experimental data, Mendel deduced that an organism has two genes (alleles) for each inherited characteristic –One characteristic comes from each parent!!! 9.3 Mendel’s principle of segregation describes the inheritance of a single characteristic P GENERATION (true-breeding parents) F 1 generation F 2 generation Purple flowersWhite flowers All plants have purple flowers Fertilization among F1 plants (F 1 x F 1 ) 3 / 4 of plants have purple flowers 1 / 4 of plants have white flowers Figure 9.3A

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A sperm or egg carries only one allele of each pair –The 2 alleles for a gene separate during gamete formation, and each gamete gets a different one –This is the law of segregation GENETIC MAKEUP (ALLELES) P PLANTS F 1 PLANTS (hybrids) F 2 PLANTS PPpp All PAll p All Pp 1/2 P1/2 P 1/2 p1/2 p Eggs P p P PP p Sperm Pp pp Gametes Phenotypic ratio 3 purple : 1 white Genotypic ratio 1 PP : 2 Pp : 1 pp Figure 9.3B

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Law of Independent Assortment Another law Mendel discovered is the Law of Independent Assortment which says that each allele segregates independently from another (traits aren’t linked unless they are on the same chromosome)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Dominant and Recessive A dominant allele is represented by a CAPITAL letter. It is always expressed when present. (BB or Bb) A recessive allele is represented by lower case letter. It is only expressed when an individual has 2, one from mom and one from dad. (bb only)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Genotype and Phenotype A genotype is the genetic make-up of an individual, expressed in letters. (BB, Bb, bb) A phenotype is the physical appearance of an individual, determined by his or her genotype. (black, brown, short, tall, etc)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Homozygous and Heterozygous Homozygous: when both alleles of a genotype are the same (either both dominant, BB, or both recessive, bb) Heterozygous: when one allele is dominant and one is recessive (Bb only)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Punnett Squares Punnett Squares are used to show the mating of two parents and the possible offspring they can produce.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Monohybrid crosses When we are looking at one trait (such as eye color or height), we do a monohybrid cross. Parents are called P Children are called F1 Grandchildren are called F2

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Purple flowers (P) are dominant to white flowers, p How would we represent a homozygous purple flower? PP A heterozygous flower? Pp What is the phenotype of a flower that is Pp? Purple What is the genotype of a white flower? pp

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Purple flowers, P, are dominant to white, p. Show a Punnett Square crossing a homozygous purple flower with a heterozygous purple flower. PP x Pp What are the genotypic and phenotypic ratios?

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Purple flowers, P, are dominant to white, p. Show a Punnett Square crossing two heterozygous flowers. Pp x Pp What are the genotypic and phenotypic ratios?

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Purple flowers, P, are dominant to white, p. Show a Punnett Square crossing a homozygous purple and homozygous white flower. PP x pp What are the genotypic and phenotypic ratios?

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Purple flowers, P, are dominant to white, p. Cross a heterozygous plant with a white plant. Pp x pp What are the genotypic and phenotypic ratios?

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Purple flowers, P, are dominant to white, p. Cross two white plants. pp x pp What are the genotypic and phenotypic ratios?

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Practice What color is PP? Pp? pp? What is the phenotype of Pp? What is the genotype of a white flower? What is the genotype of a heterozygous flower? What is the phenotype of a heterozygous flower? What is the phenotype of a homozygous recessive flower? What is the genotype of a homozygous dominant flower?

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Incomplete Dominance In incomplete dominance, the heterozygous genotype produces a phenotype that is in between the dominant and recessive ones. For example, if RR makes red flowers, and rr makes white flowers, then Rr makes PINK flowers (instead of red).

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Practice: Red flowers show incomplete dominance. RR is red, Rr is pink, and rr is white. Cross two pink flowers. Show a Punnett square and genotypic and phenotypic ratios of the offspring. Rr x Rr Cross a red flower with a white flower. RR x rr

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Blood types There are 4 possible blood types: A, B, AB, and O. A = i A i A (homozygous A) or i A i O (heterozygous A) B= i B i B (homozygous B) or i B i O (heterozygous B) AB = i A i B (always heterozygous) O = i O i O (always homozygous)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Practice. 1. Cross a woman with AB blood with a man with O blood. 2. Cross a woman with homozygous A blood with a man with AB blood. 3. Cross a woman with heterozygous B blood with a man with heterozygous A blood.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Dihybrid Crosses Instead of crossing just one trait, dihyrbrid crosses show the crossing of two separate traits.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Dihybrid examples: Dark (D) is dominant to light (d) and Brown (B) is dominant to blond (b). 1. Cross two heterozygous individuals. 2. Cross a heterozygous individual with one who is light and heterozygous for brown. 3. Cross a homozygous dark, heterozygous brown with a heterozygous dark, blond individual.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Rule of Multiplication If you flip two coins at once, the probability that both end up heads is ½ x ½ = ¼ Cross PpYyRr x Ppyyrr and calculate the probability of getting at least 2 recessive traits

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Sex-linked diseases Any gene located on a sex chromosome is called a sex-linked gene. Examples include color blindness, baldness, hemophilia, and muscular dystrophy. These recessive diseases usually affect men more than women.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –This is because the bad genes are carried on the X. Men only have one X, so one bad gene means they have the condition. Figure 9.22B-D –Women have 2 Xs, so if only one has it they are only carriers. –X R X R is a normal female –X R X r is a female who is a carrier –X r X r is an affected female –X R Y is a normal male –X r Y is an affected male R = red-eye allele r = white-eye allele

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Practice: color blindness is a recessive sex linked disease. Use the letters B and b for these problems: 1. Cross a woman who is a carrier with a normal man. 2. Cross a normal woman with a colorblind man. 3. Cross a woman who is a carrier with a color blind man.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Sex-linked recessive inherited disorders include: Color blindness Hemophilia (excessive bleeding) Muscular dystrophy (weak muscles) Male patterned baldness

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Pedigrees Pedigrees are used to trace traits through a family tree. Circles are girls, squares are boys. Filled in circles and squares represent individuals affected by a disease. A horizontal line connecting the symbols represents marriage, vertical lines represent offspring.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Turn to the pedigree on the back of your handout! The filled in circles and squares have attached earlobes. Let’s list the genotypes and phenotypes of all the individuals that we can.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Everything that’s left over… A testcross is done to figure out an unknown genotype. The mystery genotype is crossed with a homozygous recessive individual. A carrier is heterozygous for a disease but does not show symptoms. They CAN pass it on to offspring.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Other types of inheritance Pleiotropy: Genes can affect more than one phenotype (sickle-cell and malaria) Epistasis: One gene affects how a second gene is expressed Polygenic Inheritance: Many genes affect one phenotype (skin color)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Recessive inherited diseases include… Deafness Albinism Cystic fibrosis (excess mucus in lungs) PKU (mental retardation) Sickle Cell Disease (red blood cell damage) Tay Sachs (lipid accumulation in brain)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Dominant inherited diseases include… Dwarfism Alzheimer’s Huntington’s Disease (mental deterioration and tremors starting in middle age) High Cholesterol

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Fetal Screening for genetic diseases Least invasive is ultrasound, which uses sound waves to produce a picture of a fetus. In chorionic villus sampling (CVS) a narrow tube is inserted into the uterus to suction off fetal tissue, which is used for karyotyping. The most invasive is amniocentesis, in which a needle is used to withdraw amniotic fluid to test for genetic disorders.