n Labrador retriever dogs, coat color is determined by the interaction of two ge

Question

n Labrador retriever dogs, coat color is determined by the interaction of two genes (pigment and deposition of pigment). This is called epistasis. Coat color can be black (B) or brown (b) and deposition of pigment into the hair shaft is deposited (E) or not deposited (e). If a retriever has the genotype where they have _ _ ee, then they will have a yellow coat regardless of what color they inherit (e.g., Bbee or bbee gives a Yellow lab). Calculate the phenotypicratios of a cross between a male and a female Labrador retrievers that are both heterozygous for coat color and heterozygous for deposition of pigment.

c. What is the phenotypic ratio of the offspring?

Explanation / Answer

This means that both parents have recessive alleles, but exhibit the dominant phenotype. The phenotype ratio predicted for dihybrid cross is 9:3:3:1. Of the sixteen possible allele combinations: Nine combinations produce offspring with both dominant phenotypes.

They'd all show the dominant Y trait.
3/4 of them would show the R trait as well.

This is very straightforward. The former parent passes on a Y, so regardless of what the latter gives, the child has at least one Y, which yields the dominant trait.

Each parent has a 50% chance of passing on either an R or an r. So there's a 1 in 4 chance of the child being RR, and 2 in 4 chance of the child being Rr (R+r or r +R). Both these cases have at least 1 allele with the dominant case. The alternative is rr, displaying the recessive trait.

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