A colour blind girl can be born only if
Correct answer: C. her father is colour blind and her mother is at least a carrier
- A. her mother alone is colour blind
- B. her father alone is colour blind
- C. her father is colour blind and her mother is at least a carrier
- D. neither parent carries the allele
Explanation
A girl has two X chromosomes and needs the recessive allele on both, one from each parent. The father can only supply it if he is colour blind himself, and the mother must be either a carrier or colour blind. This is why affected women are rare, and it explains the pattern in which the condition seems to skip generations on the mother's side.
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About X-linked Recessive Inheritance
X-linked recessive inheritance involves genes on the X chromosome, so males express a recessive allele with no corresponding allele on their single X chromosome, while females may be carriers. Pedigrees cover haemophilia and red-green colour blindness, including carrier mothers, affected sons and the absence of father-to-son transmission.
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