Population Genetics MCAT Practice Question
A population genetics study examines a rare autosomal recessive disorder caused by loss-of-function mutations in the CFTR gene. In a coastal fishing village of 5,000 people, the disease allele frequency was 0.40 in 1960. By 2020 (15 generations later), the allele frequency decreased to 0.22. Affected individuals (homozygous recessive) have reduced fertility due to gastrointestinal complications, while heterozygous carriers are phenotypically normal with normal reproductive fitness. The village has had minimal migration and no known environmental mutagens. Which of the following best explains the change in allele frequency over this time period?
Answer choices
- ADirectional natural selection against the disease allele due to reduced reproductive fitness in homozygous individualsCorrect answer
- BGenetic drift causing random fluctuations in allele frequency in a small, isolated population
- CHeterozygote advantage conferring increased fitness to carriers in the coastal environment
- DSpontaneous new mutations converting disease alleles to wild-type at an accelerating rate
- EAssortative mating patterns causing homozygous recessive individuals to have fewer offspring
- FGene flow from neighboring populations with a lower frequency of the disease allele
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