Sickle cell disease

Sickle cell disease is a genetic blood disease seen most commonly in people of African ancestry. The disorder is caused by a single base pair change in one of the genes that codes for hemoglobin, the blood protein that carries oxygen. This abnormality causes hemoglobin to be formed improperly, and causes individual hemoglobin proteins to clump together, impairing the binding of oxygen. As a result of this mutation, the red blood cells to take on a sickle shape, rather than their characteristic donut shape. Individuals who suffer from sickle cell disease are chronically anemic and experience significant damage to their heart, lungs, and kidneys.

Sickle cell disease is determined by inheriting two recessive alleles which code for hemoglobin. If a person inherits one dominant and one recessive allele (ie heterozygous), he or she is not affected by the disease, but rather has a resistance to malaria. Inheritance of two dominant alleles, of course, causes neither the disease or any resistance to malaria.

Sources

http://www.genome.gov/glossary.cfm?key=sickle%20cell%20disease