Question

6. The white gene in Drosophila is on the X chromosome and wº (red) is dominant over w (white). A red-eyed female is crossed with a white-eyed male. (A) What must the genotype of the male be? (B) What must the genotype of the female be if the progeny are 25% red male, 25% red female, 25% white male, 25% white female?

Answer 1

6.

A.

Genotype of male will be : X^wY

This is because in male, white in color that will be expressed when even 1 copy of the gene is present in recessive gene on X chromosome.

B.Red eyed female is crossed with white eyed male

Genotype of the female would be : X^w+X^w .Only when female possess one dominant and one recessive copy of the color gene, it is possible that progeny are 25%red male, 25% red female, 25% white male and 25% white female.

This can be proved in the below punnet square:

female * male

X^w+X^w * X^wY   

male

female	Xw	Y
Xw+	Xw+Xw female red	Xw+Y male red
Xw	XwXw female white	XwY male white