Population Genetics MCAT Practice Question
A genetic screening study of 10,000 individuals from a isolated rural population identifies a recessive autosomal disorder caused by allele 'a'. The allele frequency of 'a' is 0.4 and allele 'A' is 0.6. The observed genotype frequencies are: AA = 0.36, Aa = 0.48, and aa = 0.16. When compared to expected Hardy-Weinberg equilibrium frequencies (AA = 0.36, Aa = 0.48, aa = 0.16), the population shows identical frequencies. However, detailed pedigree analysis reveals that 40% of marriages in this population are between first or second-degree relatives. Which of the following best explains the discrepancy between the pedigree findings and the genotype frequencies?
Answer choices
- AThe population is in Hardy-Weinberg equilibrium because the observed and expected genotype frequencies are identical
- BInbreeding is occurring but is masked by coincidentally matching expected HWE frequencies despite consanguineous marriagesCorrect answer
- CThe allele frequencies have been calculated incorrectly; recalculation would reveal violation of HWE
- DNatural selection against heterozygotes is balancing the effect of inbreeding
- ERecent admixture from a genetically distinct population has restored HWE despite high inbreeding coefficients
- FThe pedigree data are unreliable; consanguinity does not affect genotype frequencies under HWE assumptions
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.