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. If a vaccine for malaria was created that was 100% effective, affordable, and widely available, what would happen to the frequency of the HS allele?
A. The HS allele would decrease in regions where malaria is prevalent and remain stable in regions where malaria is absent or rare.
B. The HS allele would decrease in regions where malaria is prevalent and increase in regions where malaria is absent or rare.
C. Due to balancing selection, the frequency of the HS allele would remain stable in all regions.
D. The HS allele would increase in regions where malaria is prevalent and decrease in regions where malaria is absent or rare.
E. The HS allele would increase in regions where malaria is prevalent and remain stable in regions where malaria is absent or rare.
Answer: A
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