Schematic presentation of the ACKR1 gene, which encodes the atypical chemokine receptor 1, also called Duffy antigen receptor for chemokines (DARC). There are two Duffy alleles (FY*A and FY*B), which encode for the two Duffy blood group antigens (Fya and Fyb); they differ by a single amino acid at codon 42. The polymorphism in the promoter (–67C>T) results in loss of gene expression and produces the erythroid Duffy-null (Fy a–/b–) phenotype.