Population genetics · USMLE Step 1

A heterozygote advantage helps maintain alleles in a population by:

  1. Increasing homozygous recessive individuals
  2. Decreasing mutation rates
  3. Providing greater fitness to heterozygotes
  4. Preventing gene flow
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Correct answer: Providing greater fitness to heterozygotes

Heterozygote advantage occurs when heterozygotes have increased fitness, maintaining both alleles. Sickle cell trait is a classic example. It does not decrease mutation or gene flow.

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