The human b-globin gene has two alleles, HS and HA, individuals that are homozygous for HS have sickle-cell anemia and a lower fitness. Individuals that are heterozygotes (HSHA) do not show sickle-cell symptoms and have a resistance to malaria. Individuals that are homozygous for HA have the highest fitness but are susceptible to malaria. In areas where malaria is prevalent the HS allele is maintained in the population. Which type of selection is occurring with the b-globin gene?
A. directional
B. disruptive
C. stabilizing
D. negative frequency dependent
E. balanced
Answer: E
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