The biosynthesis of A and B antigens are catalyzed by A and B transferases, respectively. However, the common acceptor substrate of the H antigen is also produced by the reaction catalyzed by another glycosyltransferase, α1-2 fucosyltransferase. Oligosaccharide structures are generally synthesized through a series of reactions catalyzed by several glycosyltransferases, rather than a single reaction. It is, therefore, necessary to study the expression of several, if not many, glycosyltransferases in order to understand the expression of certain oligosaccharide antigens. For this purpose, we developed an experimental system to study the expression of 68 human glycosyltransferase genes (Yamamoto et al, 2003). In humans α1-3 Gal(NAc) transferase genes other than ABO genes are non-functional or have become pseudogenes during evolution. Therefore, only one gene, which is indicated by an arrow, represents this family. As you see, there are many genes encoding glycosyltransferases. They were categorized depending on which sugar is transferred. It should be noted that this table does not cover all the glycosyltransferases, though the majority of the enzymes are included.