Pedigree analysis · USMLE Step 1

Which feature on a pedigree would argue for autosomal rather than X-linked inheritance when both sexes show roughly equal affected frequency?

  1. Only male family members are ever affected
  2. Affected fathers produce only affected daughters
  3. Both sexes affected in similar proportions
  4. The trait appears only among siblings of one sex
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Correct answer: Both sexes affected in similar proportions

Roughly equal numbers of affected males and females across generations point to autosomal inheritance, whereas X-linked patterns usually show a sex bias.

Difficulty: Medium Question 18 of 19

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