In Drosophila yellow body color is caused by a sex-linked recessive allele and brown eye color is an autosomal recessive trait. A phenotypically normal female fly, heterozygous for both genes, is crossed to a male with normal body color and brown eyes. What proportion of their offspring should have yellow body color and brown eyes?

Question

Quizplus · Accepted Answer

The female is heterozygous for both traits (X^+X^y for body color and Bb for eye color), and the male is X^+Y for body color and bb for eye color. The probability of yellow body color (X^yY or X^yX^y) is 1/2, and the probability of brown eyes (bb) is 1/2. Therefore, the probability of both traits is 1/2 * 1/2 = 1/4. However, only half of the yellow-bodied offspring will also have brown eyes, so the final probability is 1/8.

In Drosophila Yellow Body Color Is Caused by a Sex-Linked