A woman who is a carrier of an X-linked recessive disease has children with an unaffected man. What proportion of their sons are expected to be affected?
Answer and explanation
Correct answer: A. 50%
- Step 1: Each son receives the mother's X chromosome, which is the normal or the mutated one with equal chance. Step 2. The father passes his Y, so a son who gets the mutated X is affected. Answer: 50%. Why not the others: 0% would need a non-carrier mother, and 100% would need an affected mother.
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