Catalyst – April 23, 2010

1. Catalyst – April 23, 2010 D = dimples, d = no dimples F = freckles, f = no freckles • Show the dihybrid cross for the following: • Female - Heterozygous for both traits • Male – Heterozygous for both traits • Give the phenotypic ratio for the cross in question 1

2. Incomplete Dominance • The phenotype of the offspring is a mixture of the two phenotypes of the parents. • Neither of the alleles is dominant to the other. • This results in a new phenotype

3. Example: Skin Color

4. Codominance • The phenotype of the offspring is a combination of the phenotypes of both parents. • Both alleles are expressed separately and contribute to the offspring’s appearance

5. Example - Chickens A black-feathered (BB) chicken crossed with a white-feathered (WW) chicken results in a black and white feathered chicken (BW).

6. Show the Cross • If a black chicken (BB) and a white chicken (WW) mate, what is that probability that the baby chicken will be black? White? Mixture? • What happens if a black and white chicken (BW) mates with another black and white chicken? What is the phenotypic ratio?

8. Incomplete Dominance?

9. Codominance?

11. Codominance?

12. Incomplete Dominance?

14. Codominance?

15. Incomplete Dominance?

16. Practice Problems Codominance: B = Black, W = White Incomplete Dominance: R = Red, Y = Yellow • Male genotype: BWRR • Female genotype: BBYY • Cross these, give the phenotypic ratio.