Final answer:
The sickle cell anemia mutation persists due to a selective advantage in malaria-endemic regions of Africa, where carriers of the mutation have increased resistance to the disease.
Step-by-step explanation:
Possible Reason for the Evolution of Sickle Cell Anemia
The mutation that causes sickle cell anemia is a single base change in the gene for human beta-hemoglobin. This mutation leads to an abnormal hemoglobin structure, and as a result, red blood cells take on a distinctive sickle or crescent shape. The presence of sickle cell anemia has persisted, especially in regions of Africa, due to a selective advantage conferred by the sickle cell trait. Individuals who are heterozygous for the mutation (carriers of one sickle cell gene and one normal gene) have increased resistance to malaria, a disease prevalent in these regions caused by the Plasmodium parasite. Malaria parasites reproduce within red blood cells, but the sickled cells are inhospitable to the parasites, thus providing the carriers with a survival advantage against malaria. Due to this advantage, the sickle cell gene remains relatively common among people of African descent despite the severe health problems associated with being homozygous for the mutation (having two copies of the sickle cell gene).
The genetic alteration in hemoglobin and the resultant sickling of red blood cells lead to complications such as anemia, organ damage, and episodes of pain. A single amino acid change—valine replacing glutamic acid in the hemoglobin protein—is responsible for this hereditary blood disorder.