Evolution and speciation · USMLE Step 1

What does the term “reproductive isolation” refer to in the context of speciation?

  1. A permanent change in the chromosome number of a population
  2. Any barrier that prevents gene flow between populations
  3. The gradual extinction of an isolated population
  4. The rapid diversification seen in adaptive radiation
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Correct answer: Any barrier that prevents gene flow between populations

Reproductive isolation includes all pre-zygotic and post-zygotic mechanisms that prevent interbreeding or viable offspring between populations — a key requirement for speciation.

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