Question: Why does the sickle cell anemia allele persist at relatively high frequencies in certain human populations? Need Assignment Help? Individuals with one copy of the allele (heterozygotes) have a survival advantage in regions where malaria is common. The allele is entirely neutral, so genetic drift maintains its frequency over time. The sickle cell allele is frequently reintroduced into populations through mutation at a high rate. The allele is dominant, leading to its increase in all human populations.