Question

Eye color in fruit flies is an X-linked character with red eyes (R) dominant to white eyes (r). The Y chromosome does not have a gene locus for eye color. What is the outcome of a mating between a red-eyed male (XRY) and a red-eyed heterozygous female (XRXr)

Answer 1

XRY X XR Xr

the gametes from the male Drosophila are XR and Y

the gametes from the female Drosophila re XR and Xr

$\left[\begin{array}{ccc}XRXR&XRY\\XRXr&XrY\end{array}\right]$

from this punnet square we can se that the genotype ratio

XRXR:XRY:XRXr:XrY is 1:1:1:1

The phenotype ratio:

red eyed female:red eyed male:white eyed male is 2:1:1