A female who carries the allele for haemophilia (X^h X^+) is crossed with a normal male (X^+ Y). Which of the following gives the correct phenotypic ratio of male offspring?

Step-by-step solution

1. Male offspring inherit their single X chromosome from the mother and the Y chromosome from the father.
2. The mother can transmit either X^h or X^+ with equal probability (½ each).
3. Hence, ½ of the sons receive X^h and are affected, while ½ receive X^+ and are normal.
4. The phenotypic ratio of affected : normal among sons is therefore 1 : 1.

Concept tested: X‑linked inheritance

Published 13 October 2026 · How this solution was prepared and checked