Sickle Cell Anaemia. That is caused by a faulty gene, totally unrelated to the gene that regulates the amount of melanin in the skin. Sickle cell anemia is an inherited disease. People who have the disease inherit two genes for sickle hemoglobin—one from each parent. Sickle hemoglobin causes red blood cells to develop a sickle, or crescent, shape. Sickle cells are stiff and sticky. They tend to block blood flow in the blood vessels of the limbs and organs. Blocked blood flow can cause pain, serious infections, and organ damage. http://www.nhlbi.nih.gov/health//dci/Diseases/Sca/SCA_Causes.html Europeans, and by extension Americans have far more recessive and faulty genes than Africans due to inbreeding, but that has nothing to do with colour either.