Population genetics · USMLE Step 1

Which situation exemplifies genetic drift?

  1. A new allele spreads due to high reproductive fitness
  2. A small group of survivors repopulates after a catastrophe
  3. Mutations continually generate new alleles
  4. Individuals prefer mating with similar phenotypes
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Correct answer: A small group of survivors repopulates after a catastrophe

A post-catastrophe small population undergoes random allele fluctuations, characteristic of drift. Fitness-driven changes represent selection. Assortative mating violates random mating.

Difficulty: Medium Question 16 of 20

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