Population genetics · USMLE Step 1

A new population is formed by 10 individuals who carry an unusually high frequency of a recessive allele. After several generations, the allele remains common. Which mechanism explains this?

  1. Genetic drift
  2. Stabilizing selection
  3. Founder effect
  4. Mutation
Show answer and explanation

Correct answer: Founder effect

The founder effect occurs when a new population begins with a small group that carries different allele frequencies than the original population. This can make rare alleles common. Drift may amplify the effect but is not the primary explanation here.

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