Population Genetics MCAT Practice Question
A genetic counselor is evaluating a rare autosomal recessive disorder (cystic fibrosis-like phenotype) in an isolated Amish community of approximately 45 unrelated families. Over the past 3 generations, the frequency of a specific loss-of-function mutation has increased from 12% to 67% in the population, despite no evidence of reproductive advantage for carriers. The counselor notes that all affected individuals can trace their ancestry to a single founder couple who immigrated 6 generations ago. Genetic testing reveals no new mutations, and heterozygous carriers show no phenotypic difference from wild-type homozygotes. Which evolutionary mechanism best explains the high frequency of this mutation in this population?
Answer choices
- APositive natural selection favoring heterozygous carriers
- BRecurrent de novo mutations in the founder lineage
- CGene flow from neighboring populations with higher allele frequency
- DGenetic drift following a founder effectCorrect answer
- EInbreeding depression selecting against homozygous recessive individuals
- FBalancing selection maintaining both alleles at intermediate frequencies
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