Mendelian inheritance · USMLE Step 1

Two unaffected parents have a child with an autosomal recessive disease. What is the probability that their next child will be a carrier?

  1. 25%
  2. 33%
  3. 50%
  4. 75%
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Correct answer: 50%

Two carriers have offspring with genotypes: 25% affected, 50% carriers, 25% unaffected non-carriers. Thus, there is a 50% chance the next child is a carrier.

Difficulty: Medium Question 11 of 20

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