You cross a purebreeding yellow-eyed male fly with a purebreeding red-eyed female fly. The resulting offspring are red. When you cross F1 males back to a pure-breeding yellow female, you get yellow males, while when you cross F1 males back to pure-breeding red
female you get red males.

(a) What simple model accounts for this?

(b) Given your model from (a) what are the expected eye colors (and their frequencies) in the F1 when the purebreeding yellow fly is a male and the purebreeding red fly a female?

(c) Now suppose the sexes are switched, so that the male is purebreeding red and the female purebreeding yellow.