Glycotransferases, produced by multiple genes form the I and i antigens. The I and i antigens are on the ABH oligosaccharide precursor chains. The I antigen is associated with the branched structure while i is associated with the linear structure. Therefore, the antigens can be found in both secretions and on the red blood cell membrane. I and i are not alleles and are not described as a phenotype. An individual is either positive or negative for these antigens.