In fruit flies, red-eyes are dominant to white-eyes. In addition, eye color is a sex-linked trait. A red-eyed male Drosophila mates with a red-eyed female Drosophila. One of the female's parents had white eyes. What proportion of the male offspring will have white eyes?
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%

Question

Quizplus · Accepted Answer

Since eye color is a sex-linked trait located on the X chromosome and the female has a red eye but one parent with white eyes, she must be heterozygous (X^RX^w). The male, having red eyes and only one X chromosome, has the genotype X^RY. When they mate, half of the male offspring will inherit the X^w from the mother and the Y from the father, resulting in white eyes. Therefore, 50% of the male offspring will have white eyes.

In Fruit Flies, Red-Eyes Are Dominant to White-Eyes