Pedigree analysis · USMLE Step 1

In autosomal dominant inheritance with full penetrance, what is the probability a child will be affected if one parent is heterozygous (Aa) and the other is homozygous normal (aa)?

  1. 0%
  2. 25%
  3. 50%
  4. 100%
Show answer and explanation

Correct answer: 50%

In autosomal dominant inheritance, a heterozygous parent (Aa) crossed with a homozygous normal parent (aa) gives each child a 50% chance of inheriting the mutant allele and being affected.

Difficulty: Medium Question 7 of 19

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