In malaria-endemic regions, the sickle cell allele persists at intermediate frequency because
- A
Mutation rate continuously regenerates the allele each generation
- Bcheck_circle
Heterozygotes (HbAS) have higher fitness than either homozygote
- C
homozygotes have higher fitness than in dry seasons
- D
is dominant and confers no fitness cost
Explanation
HbAS heterozygotes resist malaria but lack severe sickle-cell disease (HbSS lethal early). Balanced polymorphism: heterozygote advantage maintains both alleles at equilibrium.