A pure bred black dog was crossed to a pure bred white dog T

A pure bred black dog was crossed to a pure bred white dog. The F1 puppies were all black. When the F1 dogs were crossed to each other, the phenotypes observed in the F2 were as follows: Black dogs = 275 White dogs = 67 Black spotted dog = 20 What is the most likely explanation for these results? Select one: a. The alleles are codominant b. There are two genes that show recessive epistasis c. There are two alleles that show dominant epistasis d. There are two genes that show incomplete dominance e. None of the above

Solution

I think the answer is e. None of the above.

Epistasis causes masking of one gene by the effect of another gene at different locus. Here only one gene is involved and no epistatic gene interaction occurs.

These alleles are not codominant. If they are codominant, F1 progeny should not be black. Incomplete dominance results in intermediate coloured F1 progeny.

The reason may be variable expressivity. Individuals with same genotype can also show different degrees of the same phenotype.