Question

In fruit flies, the gene for eye color is located on the X chromosome, and the red eye allele is dominant over the white eye allele A female fly with genotype XRXr is mated with a male fly with genotype XrY. Which statement below best describes the expected outcome of this cross?

Answer 1

Answer:

b. The chance of an offspring having white eyes is 50%.

Explanation:

a. The chance of an offspring having red eyes is 75%.

b. The chance of an offspring having white eyes is 50%.

c. The chance that a male offspring will have white eyes is 0%.

d. The chance that a female offspring will have red eyes is 100%.

Gene for eye color is X-linked.

Red allele R is dominant over white allele r.

$X^RX^r$ female is crossed with $X^rY$ male:

$X^RX^r$   x   $X^rY$   =  $X^RX^r, X^RY, X^rX^r and X^rY$

50% of the offspring has red eye ($X^RX^r and X^RY$) while the remaining 50% has white eye ($X^rX^r and X^rY$).

Hence,

The chance of an offspring having white eye is 50%

The chance of an offspring having red eye is 50%

The chance of  a male offspring having white eye is 50% and not 0%

The chance of a female offspring having red eye is 50% and not 100%

The correct option is b.