Mendelian inheritance · USMLE Step 1

A woman affected by an autosomal dominant condition has a child with an unaffected man. What is the probability that their child will be unaffected and also a non-carrier?

  1. 25%
  2. 50%
  3. 75%
  4. 100%
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Correct answer: 50%

A heterozygous affected mother passes the mutant allele to 50% of children. The other 50% inherit the normal allele and are fully unaffected. There are no carriers in dominant conditions.

Difficulty: Medium Question 17 of 20

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