In Duchenne muscular dystrophy (X-linked recessive), if the MOTHER IS A CARRIER and the FATHER IS UNAFFECTED — what percentage of MALE children will have the disease?

Correct answer: C. 50% (half the sons will be affected)

• A. 75% is incorrect for any X-linked recessive inheritance pattern.
• B. 25% would be the probability for the ENTIRE offspring population (all children), not specifically sons.
• C. Correct. X-linked recessive: Mother = X^DMD X (carrier) × Father = X Y (unaffected). Sons (XY): X^DMD Y = AFFECTED (Duchenne) or X Y = unaffected → 50% of sons are affected. Daughters (XX): X^DMD X = CARRIERS or X X = unaffected → 50% of daughters are carriers, 0% affected. Total: 25% of ALL children will have DMD (25% of total = 50% of sons only).
• D. 100% would require the father to also be affected (X^DMD Y).