Evolution and speciation · USMLE Step 1

In allopatric speciation, which force tends to contribute most to genetic divergence between the geographically separated populations?

  1. Ongoing gene flow between the populations
  2. Genetic drift together with natural selection
  3. Somatic mutation in non-reproductive cells
  4. Horizontal gene transfer between individuals
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Correct answer: Genetic drift together with natural selection

Once gene flow is blocked by geographic separation, genetic drift and natural selection act independently in each isolated population, promoting divergence in allele frequencies and phenotypes over time.

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