Catalyst – April 23, 2010 D = dimples, d = no dimplesF = freckles, f = no freckles
1. Show the dihybrid cross for the following:• Female - Heterozygous for both traits• Male – Heterozygous for both traits
2. Give the phenotypic ratio for the cross in question 1
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
Example: Skin Color
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
Example - Chickens
A black-feathered (BB) chicken crossed with a white-feathered (WW) chicken results in a black and white feathered chicken (BW).
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?
Incomplete Dominance?
Codominance?
Codominance?
Incomplete Dominance?
Codominance?
Incomplete Dominance?
Practice Problems
Codominance: B = Black, W = WhiteIncomplete Dominance: R = Red, Y = Yellow
• Male genotype: BWRR• Female genotype: BBYY• Cross these, give the phenotypic ratio.