Variations in Populations

AP Biology· difficulty 2/5

Generations freq(A) ~0.5

A population stabilizes p near 0.5 over time, as in heterozygote-advantage scenarios (e.g., sickle-cell HbS in malaria zones). This pattern is

  • A

    Directional selection toward fixation

  • B

    Bottleneck effect

  • C

    Balancing selection maintaining polymorphism

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  • D

    Genetic drift to fixation

Explanation

Balancing selection (such as heterozygote advantage) maintains both alleles at intermediate frequencies because heterozygotes have higher fitness, preventing fixation of either allele.

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