Why does the mutation that causes sickle cell anaemia also give protection from malaria?
Malaria is a parasitic infection of the red blood cells by any of several species of the genus Plasmodium. The infection is obtained through the bite of an Anopheles mosquito that has previously drawn blood from an infected individual. The proboscis (needle nose) of the mosquito serves the role of carrier or vector like a dirty needle does for AIDS. Eventually, the parasite enters the red cell, reproduces, and ultimately breaks open the red cell to go infect more cells. Healthy red cells look like lozenges. Sickle cells are the shape of fingernail clippings and are immune to the Plasmodia. People with sickle cell anemia, the homozygous form of the disease, often die of the sickle cell disease, not malaria. But heterozygous individuals, with one allele affected and one normal, have sickle cell trait, and are also protected because enough of their cells sickle under physical stress. Sickle cells are too sick for the parasite.
