A patient has Duchenne muscular dystrophy. The mother is a carrier and the father is unaffected. What percentage of the FEMALE siblings are expected to be carriers?

Correct answer: C. 50%

• A. 100% would only apply if the mother were affected (X^D X^D) — she is a carrier (X^D X), not affected.
• B. 75% would apply if both parents contributed to the risk — not the case in X-linked.
• C. Duchenne muscular dystrophy is X-linked recessive. The mother is a carrier (X^D X). The father is unaffected (X Y). Female offspring: 50% receive the maternal X^D (carrier) and 50% receive the normal maternal X. Therefore, 50% of female siblings will be carriers.
• D. 25% applies to certain autosomal recessive inheritance patterns — not X-linked recessive.