C/CPublished research associates this genotype with typical Duffy antigen expression on red blood cells.
C/TOne copy of the variant. Published research associates this genotype with reduced Duffy antigen expression.
T/TPublished research associates this genotype with absence of the Duffy antigen on red blood cells (the "Duffy-null" phenotype) — this is common in populations of West African ancestry and is associated with natural resistance to Plasmodium vivax malaria infection, since that parasite uses the Duffy antigen to enter red blood cells.
Source: Miller et al. 1976, New England Journal of Medicine — the Duffy blood group phenotype and resistance to Plasmodium vivax malaria.