Duffy System

Common alleles in the the Duffy blood type are the Fy^a and Fy^b antigens. In the Caucasian population, Fy^a has a frequency of 66% and Fy^b has a frequency of 83%. In those of African ancestry, the null phenotype (Fy^a-b-) is very common (68%) due to a mutation in the GATA-promoter region upstream of the Fy^b allele.

Because this mutation prevents only erythroid-expression of Fy antigens, Black individuals with the (Fy^a-b-) are at risk of making Fy^a but not Fy^b antibodies.

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