Studying Heredity Chapter 8 Section 8-3

Objectives for section 8-3 Predict results of genetic crosses w/Punnett Square Describe how a testcross can be used to determine genotype Define & analyze a simple pedigree PG. 170

Punnett Square predicts possible outcomes of genetic crosses Inventor– Reginald Punnett

Monohybrid Cross 1. Assign letters for traits 2. Determine parents’ genotypes 3. Write genotypes across top & side 4. Fill in each box of the Punnett square 5. State genotype and phenotype

A heterozygous dimpled female marries a heterozygous male A heterozygous dimpled female marries a heterozygous male. What are the possible outcomes of their children? D

Test cross: dominant phenotype/unknown genotype (x) w/ homozygous recessive Breeders need to know if organism- heterozygous/ homozygous dominant for a character Why?

EX: A plant w/ yellow seeds & unknown genotype (Y EX: A plant w/ yellow seeds & unknown genotype (Y?) is test crossed with a plant that has green seeds (yy).

V. Dihybrid Crosses =2 contrasting traits Cross 2 pea plants heterozygous for seed shape AND seed color 1. R=round r=wrinkled AND Y=yellow y=green 2. Parents’ genotypes a. RrYy x RrYy 3. Possible Gametes?? a. RY, Ry, rY, ry

Typical Dihybrid Cross 4. Phenotypic ratio 9 round, yellow 3 round, green 3 wrinkled, yellow 1 wrinkled green Typical dihybrid cross ratio: 9:3:3:1

Monohybrid vs. Dihybrid Cross Monohybrid: involves one trait with a phenotypic ratio for the F2 generation of 3:1 Dihybrid: involves two traits with a phenotypic ratio for the F2 generation of 9:3:3:1

Why use Punnett Squares? A. Improve crops B. Improve domestic animals C. Determine risk for genetic disorders D. Predict expected results of genotypes or phenotypes

Probability –likelihood that a specific event will occur A. Expressed in words, decimals, fractions, or percentages B. Probability= # of 1 kind of possible outcome/total # of all possible outcomes C. Both parents must be considered when calculating probability D. To find probability, multiply the separate probabilities of the two events

Pedigree: family history-shows a trait inherited over several generations Helps in tracking genetic disorders ♀ ♂ Colorblindness Pedigree

What is determined from a pedigree? Autosomal: gene will appear in both sexes equally Sex-linked: allele located only on the X chromosome & are recessive a. Males carrying recessive allele on X chromosome exhibit sex-linked character…Why?? b. Females-less chance of exhibiting sex-linked condition…Why??

♂ Pedigree for the Albino Trait ♀ autosomal Pedigree for Hemophilia Sex linked!! Only ♂ affected

3. Autosomal Dominant: every individual w/condition has a parent w/condition 4. Recessive: individual w/ condition can have 1, 2, or neither parent exhibit the condition

5. Homozygous dominant or. heterozygous: phenotype will show 5. Homozygous dominant or heterozygous: phenotype will show the dominant allele 6. Homozygous recessive: phenotype shows the recessive allele Can 2 people who are heterozygous carriers of a recessive mutation have children with the mutation??

Hemophilia-the Royal disease 1 in 10,000 ♂ 1 in 100,000,000 ♀