The H gene encodes an enzyme that is required in the expression of the H antigen on the surface of red blood cells. Translation of the active allele, H, of the FUT1 gene results in formation of the enzyme known as α-1,2-fucosyltransferase (H is also known as FUT1 because the gene product is a FUcosyl Transferase). This enzyme acts to transfer a fucose sugar onto a special precursor on the surface of the RBC known as a “type 2” chain. Fucose is added to the last sugar on that chain, galactose, and the chain expresses the H antigen as a result. Note that H has similarities and distinct differences from the gene known as Se (FUT2, or “secretor”).