The mutation for sickle-cell anemia is a recessive genetic disease but also causes resistance to malaria when present. Based on this information, which combination of the following statements regarding phenomena of genetic variation does this represent?
1 A product of frequency-dependent selection, because if the recessive allele is being paired with another dominant allele and becomes too common, it could result in an increase in severe sickle-cell homozygotes with no malaria resistance
2 A heterozygote advantage, because being homozygous with the mutation means severe sickle-cell anemia, while being homozygous without it means susceptibility to malaria
3 A product of geographical variation, because the species would have evolved resistance based on an environment with malaria in some areas, but would not have in others
4 A product of diversifying selection, because individuals possessing both extremes of this phenotype are favored over individuals possessing intermediate phenotypes
A)1 and 2
B) 1, 2, and 3
C) 2 and 3
D) 2, 3, and 4
