Refer figure 20-17. The occurrence of the alleles at the Duffy blood group locus differs extensively in human populations. The Duffy locus (Fy) encodes a glycoprotein that functions as a receptor for multiple intercellular signalling proteins. Most of the local population in sub-Saharan Africa carries the Fynull allele that does not express any of the Duffy glycoprotein on the red blood cells, though the protein is still being formed in other cell types.
The molecular description for the lack of Duffy glycoprotein expression on the red blood cells is the occurrence of a point mutation in the promoter region of the Duffy gene at position -46. Mutation stays in a binding site for the transcription factor particular to red blood cells called GATA1. The activity of the Duffy gene enhancer in reporter gene assays stops due to the mutation of the site.
The GATA sequence triggers Duffy gene expression, which is particular to red blood cells that result in the Duffy protein on the red blood cells surface. Plasmodium vivax, which is a malaria parasite, attacks red blood cells by using Duffy protein as a recognition site. The mutation GACA stops the binding of the GATA1 protein to the Duffy gene enhancer and inhibits the expression of Duffy protein on the red blood cells. The deficiency of Duffy protein specifies that Plasmodium vivax no longer capable to identify and infect the red blood cells and hence, confers the resistance to malaria.