and a low prevalence in two others. In the Yemenite Jews the frequency of the Fy allele is 0.5879 The frequency of this allele varies from 0.1083 to 0.2191 among Jews from the Middle East, North Africa and Southern Europe. The incidence of Fya among Ashkenazi Jews is 0.44 and among the non-Ashkenazi Jews it is 0.33. The incidence of Fyb is higher in both groups with frequencies of 0.53 and 0.64 respectively. In the Chinese ethnic populations—the Han and the She people—the frequencies of Fya and Fyb alleles were 0.94 and 0.06 and 0.98 and 0.02 respectively. The frequency of the Fya allele in most Asian populations is ~95%. In Grande Comore (also known as Ngazidja) the frequency of the Fy(a- b-) phenotype is 0.86. The incidence of Fy(a+b-) in northern India among blood donors is 43.85%. In the Maghreb, Horn of Africa and the Nile Valley, the Afroasiatic (Hamitic-Semitic) speaking populations are largely Duffy-positive. Between 70%-98% of Hamito-Semitic groups in Ethiopia were found to be Duffy-positive. Serological and DNA based analysis of 115 unrelated Tunisians also found an FY*X frequency of 0.0174; FY*1 = 0.291 (expressed 0.260, silent 0.031); FY*2 = 0.709 (expressed 0.427; silent 0.282). Since the FY*2 silent is the most common allele in West Africa, its minor occurrence in the sample probably represents recent diffusion from the latter region. In Nouakchott, Mauritania overall 27% of the population are Duffy-positive. 54% of Moors are Duffy antigen positive, while only 2% of black ethnic groups (mainly Poular, Soninke and Wolof) are Duffy positive. A map of the Duffy antigen distribution has been produced. The most prevalent allele globally is FY*A. Across sub-Saharan Africa the predominant allele is the silent FY*BES variant. In Iran the Fy (a-b-) phenotype was found in 3.4%. There appears to have been a selective sweep in Africa which reduced the incidence of this antigen there. This sweep appears to have occurred between 6,500 and 97,200 years ago (95% confidence interval) The distribution within India has been studied in some detail. Clinical significance Historically the role of this antigen other than its importance as a receptor for Plasmodium protozoa has not been appreciated. Recent work has identified a number of additional roles for this protein. Malaria On erythrocytes, the Duffy antigen acts as a receptor for invasion by the human malarial parasites P. vivax and P. knowlesi. This was first shown in 1980. Duffy