The fucosyltransferase 2 gene FUT2 (secretor status) confers the ability to secrete the ABO blood group antigen. It also affects Lewis antigen status.
FUT2 has active (Se) and non-secretory (se) alleles; Secretory status is dominant. Phenotype affects immunity to norovirus and influenza. Recessive (sese) carriers are resistant to the Norwalk strain.