You are performing a fruit fly cross similar to those that Morgan performed. Unfortunately, you forgot to write down the parents of your cross. You count the progeny, and find you have 40 red-eyed males, 80 red-eyed females, and 40 white-eyed males. Assuming that all genotypes from this cross should have equal survival rates, what are the genotypes of the parent flies?

The allele expressing red color (wild) is dominant over the allele expressing white color (mutant)
F1 Progeny: 40 red-eyed males, 80 red-eyed females, and 40 white-eyed males

Red-eyed males--> X⁺Y

Red-eyed males--> X⁺X⁺

White-eyed males-->X⁻Y

Being X⁺ the one that expresses red eyes and X⁻ the one that expresses white eyes.

Individuals with Red eyes: 40 males + 80 females = 120 red-eyed individuals

Individuals with white eyes: 40 males

This is a proportion 3:1 ----> 120 red: 40 white

There were red and white-eyed males, which Suggesting that the female parental was heterozygous for the color-eye trait, giving one X⁺ to 40 males and X⁻ to the other 40 males.

While the parental male was red-eyed. If it was white-eyed, then white-eyed females would have appeared among the offspring.

Parental) X⁺X⁻ x X⁺Y

Punnet square) X⁺ X⁻

X⁺ X⁺X⁺ X⁺X⁻

Y X⁺Y X⁻ Y

F1) 1/4 X⁺X⁺

1/4 X⁺X⁻

1/4 X⁺Y

1/4 X⁻ Y

2/4 red-eyed females

1/4 red- eyed male

1/4 white-eyed male

3/4 red-eyed individuals

1/4 white- eyed individuals