A colour‑blindness (X‑linked recessive) gene is represented by ‘c’. If a normal‑vision male (XY) marries a carrier female (XcX), what is the expected proportion of colour‑blind sons?

Step-by-step solution

1. Identify the sex chromosomes of the parents: male contributes either X or Y, female contributes X or c.
2. List the possible sperm: X (carrying normal allele) or Y (no allele for the trait).
3. List the possible eggs: X (normal) or c (carrier).
4. Form the combinations for sons (require Y sperm): Y (from father) + X (normal egg) gives a normal son, Y + c (carrier egg) gives a colour‑blind son.
5. Thus, out of the two possible son genotypes, one is colour‑blind, giving a probability of 1/2 or 50%.
6. Therefore, 50% of the sons are expected to be colour‑blind.

Concept tested: Sex‑linked inheritance

Published 21 August 2026 · How this solution was prepared and checked

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