Question

In fruit flies, gray body color (b) is dominant over black body color. When crossing a homozygous dominant gray fly with a black fly, the offspring will be:

a) All gray
b) All black
c) All heterozygous
d) All phenotypically distinct

Answer 1

When true-breeding or homozygous individuals that differ for a certain trait are crossed, the F₂ offspring will exhibit a ratio of three dominant to one recessive.

Step-by-step explanation:

When true-breeding or homozygous individuals that differ for a certain trait are crossed, all of the offspring will be heterozygotes for that trait. If the traits are inherited as dominant and recessive, the F₁ offspring will all exhibit the same phenotype as the parent homozygous for the dominant trait. If these heterozygous offspring are self-crossed, the resulting F₂ offspring will be equally likely to inherit gametes carrying the dominant or recessive trait, giving rise to offspring of which one quarter are homozygous dominant, half are heterozygous, and one quarter are homozygous recessive. Because homozygous dominant and heterozygous individuals are phenotypically identical, the observed traits in the F₂ offspring will exhibit a ratio of three dominant to one recessive.