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MCAT Question A Day - 5/9/13 - Answer!

According to the Hardy-Weinberg theorem, which of the following conditions would not contribute to gene frequencies in a population remaining in equilibrium?

A.  Absence of natural selection
B.  Absence of a large breeding population
C.  Absence of migration
D.  Absence of mutation

The correct answer is (B). When a breeding population is relatively small, chance events can lead to changes in gene frequencies (genetic drift). Thus, the population would not remain at equilibrium and would “evolve.” The other choices all reflect conditions that lead to gene frequencies remaining unchanged.