Mendelian inheritance · USMLE Step 1

A pedigree shows only males affected, with no male-to-male transmission. This most likely represents:

  1. Autosomal dominant
  2. Autosomal recessive
  3. X-linked recessive
  4. Mitochondrial
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Correct answer: X-linked recessive

X-linked recessive traits affect males disproportionately and lack male-to-male transmission. Females are usually carriers. Autosomal traits do not show this pattern.

Difficulty: Medium Question 18 of 20

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