Se gene, also called FUT2 https://www.ncbi.nlm.nih.gov/gene/2524;
Together with the Lewis blood group gene, the Se gene regulates presence and concentrations of fucosylated human milk oligosaccharides. Both genes encode for fucosyltransferase, enzymes that add fucose to an oligosaccharide and are well known to control blood group antigens (Dotz and Wuhrer 2016). The Se gene encodes for fucosyltransferase‑2.
Women with active Se gene express fucosyltransferase-2 which marks them as "secretors". If the gene is inactive, the enzyme is absent and individuals are described as non‑secretors. The four combinations of secretor/non‑secretor status and Le-positive/negative were first described as four global milk groups in 1997 (Thurl et al. 1997).