Migrant Populations and the Diffusion of the Sickle-Cell Gene

If we assume that the sickle-cell mutation occurred in equatorial Africa, distribution of the sickle-cell trait in the Middle East and India correlates well with historical evidence of population displacement into these areas as a result of the East African slave trade, and with the distribution of African blood group markers in Asia. The occurrence of the sickle-cell trait in southern Europe parallels the extent of the medieval Arab conquests and is believed to reflect gene flow from the Middle East. Changing endemicity of Plasmodium falciparum malaria; interaction between hemoglobin S, thalassemia, and glucose-6-phosphate dehydrogenase deficiency; and contribution to the gene pool from subjects with mild homozygous sickle-cell disease are thought to be additional reasons for patterns of sickle-cell trait distribution in Eurasian populations.