Sickle cell anemia is caused by a point mutation in the gene coding for hemoglobin. this point mutation causes an abnormal form of the protein hemoglobin. individuals who are heterozygous for normal hemoglobin and the mutation experience varying degrees of sickle cell anemia. however, they have increased resistance to the disease individuals homozygous for either normal or sickle cell mutation have increased morbidity and mortality where this disease is endemic. this is an example of