Evolution and speciation · USMLE Step 1

What effect does genetic drift most strongly have on a population?

  1. Consistently favoring beneficial alleles over deleterious ones
  2. Randomly altering allele frequencies, mainly in small populations
  3. Increasing gene flow and mixing between separate populations
  4. Generating entirely new mutations in the gene pool
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Correct answer: Randomly altering allele frequencies, mainly in small populations

Genetic drift causes random fluctuations in allele frequencies, and its impact is greatest in small populations where sampling effects are more pronounced.

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