Explanation

Sickle cell anemia (in which RBCs become sickle-shaped and stiff) is a genetic disorder that is autosomal and linked to a recessive allele. It has not been eliminated from the African population because it provides immunity against malaria. People who are heterozygous for sickle cell allele are much less susceptible for falciparum malaria, which is one of main cause of illness and death in them. Thus, the sickle cell allele is maintained at high levels in populations where falciparum malaria is common.