Mendelian inheritance · USMLE Step 1

If a homozygous recessive individual mates with a heterozygous carrier, what percentage of their offspring are expected to be affected?

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

Correct answer: 50%

The cross rr × Rr results in 50% rr offspring. These individuals express the recessive phenotype. The remaining 50% are carriers.

Difficulty: Medium Question 7 of 20

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