A woman is a carrier of Duchenne muscular dystrophy and her partner is unaffected. What is the chance that a son is affected?
Answer and explanation
Correct answer: B. 1 in 2
- Step 1: Duchenne is X-linked recessive, with the mutation passed on the X chromosome. Step 2. A carrier mother passes the affected X to half of her sons, who are affected, and half of her daughters, who become carriers. Answer: 1 in 2. Why not the others: One in 4 describes autosomal recessive risk. Daughters of an unaffected father are carriers or unaffected, not affected. The gene is on the X chromosome.
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