88. In Drosophila, the gene for eye colour is present on the X chromosome. When a red-eyed
female was mated with a white-eyed male, a total of 100 progeny were obtained – 50 females and
50 males. Of the 50 females, 25 were red-eyed, and 25 were white-eyed. How many of the male
progeny were red-eyed?
(A) 0
(B) 10
(C) 20
(D) 25

Drosophila X-linked eye color inheritance results in no red-eyed males from a red-eyed female crossed with a white-eyed male when progeny show 50:50 female eye colors.​

Correct Answer

(A) 0​

Genetic Basis

The eye color gene lies on the X chromosome, with red (X^R, dominant) over white (X^r, recessive). Males are XY (hemizygous), expressing their single X allele; females are XX. The red-eyed female produces 25 red-eyed and 25 white-eyed daughters (50:50), indicating she is heterozygous (X^R X^r). The white-eyed male is X^r Y.​

Punnett Square

Female gametes: 50% X^R, 50% X^r. Male gametes: 50% X^r, 50% Y.

Each cell represents 25 progeny. All 50 males get X^r from mother and Y from father, yielding white-eyed males only. Daughters split 50:50 red/white per data.​

Option Analysis

• (A) 0: Correct. Males inherit mother’s X^r allele exclusively, showing recessive white eyes.​

• (B) 10: Incorrect. Assumes ~20% red males, ignoring X-linked pattern and 50:50 female split.​

• (C) 20: Incorrect. Suggests 40% red males, mismatched with hemizygous male inheritance.​

• (D) 25: Incorrect. Implies 50% red males (autosomal-like), but X-linkage prevents paternal X^R transmission to sons.​