Duffy blood group and hemoglobin variants.

Data on a sample of 809 Afro-Americans indicated that there is no association between Duffy null (a-,b-) blood type and sickle cell trait. The results further rule out close linkage as an alternative hypothesis to explain the reported association between these loci in areas where falciparum and vivax malaria are endemic and indicate that, even if the two loci are independent or loosely linked, direct evidence of the selection favoring AS Fy-Fy- individuals must come from populations where mixed malaria infections occur. Stratification, as an explanation for the reported association, is also discussed.