Question

If a male fly hemizygous for the recessive X-linked white mutation (w) is mated to a female fly heterozygous for white, and the phenotypically white F1 are intercrossed, which will be true:
a. Half of both the F2 males and females are red
b. All of the F2 are red All of the F2 males are red, all of the F2 females are white
c. All of the F2 are white
d. All of the F2 males are white, all of the F2 females are red

Answer 1

Answer:

c. All of the F2 are white

Explanation:

The white mutation is recessive and located in the X chromosome.

White male fly

Genotype: XʷY

Gametes: Xʷ and Y

Heterozygous female fly

Genotype: Xʷ⁺Xʷ

Gametes: Xʷ⁺ and Xʷ

Possible F1 genotypes and phenotypes:

• Xʷ Xʷ⁺ : female wild-type
• XʷXʷ : female white
• Xʷ⁺Y: male wild-type
• Xʷ Y: male white

The white F1 indiviudals are:

Female XʷXʷ . Gametes: Xʷ

Male XʷY. Gametes: Xʷ and Y

Possible F2:

• XʷXʷ
• XʷY

All F2 are white.