Duffy System

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

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

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