Genetic and Pediatric Diseases · USMLE Step 1

In a pedigree showing an X-linked recessive disease such as Duchenne muscular dystrophy, which parent transmits the defective gene to an affected male child?

  1. Father only
  2. Mother only
  3. Both parents equally
  4. Impossible to determine
Show answer and explanation

Correct answer: Mother only

X-linked recessive diseases are transmitted by carrier mothers; an affected male receives the mutant X chromosome from his mother, while the father contributes Y.

Difficulty: Medium Question 13 of 20

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