Simple Punnett Square Warm-up

1. Simple Punnett Square Warm-up • In cats, long hair is recessive to short hair. A true-breeding (homozygous) short-haired male is mated to a long-haired female. What is the genotypic and phenotypic ratios for their offspring?

2. Simple Punnett Square Warm-Up • Mr. and Mrs. Miller both have widow’s peaks (dominant). Their first child also has a widow’s peak, but their second child doesn’t. Mr. Miller accuses Mrs. Miller of being unfaithful to him. Is he necessarily justified? Why or why not? Use a Punnett square to defend your response.

3. Independent Assortment

4. Two-Factor Crosses: F1 • Mendel crossed true-breeding plants that produced only round yellow peas (genotype RRYY) with plants that produced wrinkled green peas (genotype rryy) • All of the F1 offspring produced round yellow peas. What does this show? • This shows that the alleles for yellow and round peas are dominant over the alleles for green and wrinkled peas.

5. Two Factor Crosses: F2 • Mendel knew the genotypes of the F1 generation were RrYy. All heterozygous for seed shape and seed color genes. • When he crossed these F1 plants he found that in the F2 generation, there were plants that had combinations of phenotypes (combos of alleles) not found in either parent. • Therefore, the alleles had segregated independently of each other. • We call these tests two-factor or dihybrid crosses.

6. Independent Assortment

7. Independent Assortment • The Principle of Independent Assortment states that genes for different traits can segregate independently during the formation of gametes. • Independent assortment helps account for the many genetic variations observed in plants, animals, etc. • Example:Blue eyes and brown hair; one dominant and one recessive trait are visible in phenotype. The dominance of brown hair had no bearing on the expression of blue eyes.

8. Setting Up a Dihybrid Cross • In cats long hair is dominant to short hair and short tail is dominant to long tail. A long-tailed male cat that is heterozygous for hair length is mated with a female cat who is heterozygous for both traits. What are the genotypic and phenotypic ratios for their kittens? • First step: Write out genotypes of both parents.

9. Setting Up a Dihybrid Cross • Parents genotypes – (H for hair-length; T for tail-length) • Male: Hhtt • Female: HhTt • Second Step: Figure out all possible combinations (Independent Assortment). Use FOIL method to determine combinations. • FOIL (First, Outside, Inside, Last)

10. Setting Up a Dihybrid Cross Male Gametes • Possible combinations (should be four for each) • Male: Ht, Ht, ht, ht • Female: HT, Ht, hT, ht • Third Step: Take the four combinations for each parent and put them on the outside of your dihybridPunnett square. Female Gametes

11. Fourth Step: Fill in Punnett square Long-hair, short-tail

12. Setting Up a Dihybrid Cross • Fifth step: Tally up all the different genotypes and phenotypes from the cross. • Determine the probability of each genotype/phenotype and right it down as a ratio (ex. 9:3:3:1).

13. Setting Up a Dihybrid Cross • Genotypes • HHTt: 2 • HHtt: 2 • HhTt: 4 • Hhtt: 4 • hhTt: 2 • hhtt: 2 • Phenotypes • Long hair, Short tail: 6 • Long hair, Long tail: 6 • Short hair, Short tail: 2 • Short hair, Long tail: 2 • Phenotypic Ratio: 6:6:2:2 or 3:3:1:1