Why is the incidence of sickle-cell anemia an excellent example of a balanced polymorphism, in which two or more alleles are maintained by natural selection in a population?

Balanced polymorphism is an occurrence where different phenotypes are maintained at relatively stable frequencies

in the population.

Sickle-cell anemia is a result from a change in the hemoglobin molecule structure. Sickle-cell are red blood cells that are misshapen, reducing their ability to carry oxygen, resulting to anemia.

The quantities of normal and sickled

cells are roughly equal in the heterozygous state. The relatively unchanging frequencies of the sickle-cell heterozygotes and homozygous genotypes make them an excellent example of balanced polymorphism.