Sickle cell anemia a hereditary disease in which a mutation in the gene for one of the proteins that comprises hemoglobin results in the formation of defective hemoglobin molecules known as hemoglobin S. Individuals who are homozygous for this mutation (possess two genes for hemoglobin S) have red blood cells that change from the normal discoid shape to a sickle shape when the oxygen supply is low. These sickle-shaped cells are easily trapped in capillaries and damaged, resulting in severe anemia. Individuals who are heterozygous for the mutation (possess one gene for hemoglobin S and one normal hemoglobin gene) have increased resistance to malaria. |
