Scheme representing the biosynthesis of P^k, P and P1 antigens and some other related structures, such as the blood group H, A, and B antigens. The symbols used follow the recommendations of Varki et al;⁵⁰  ie, glucose (▴), N-acetylglucosamine (■), galactose (●), N-acetylgalactosamine (□), fucose (Δ), and sialic acid (♦). Ceramide is abbreviated to Cer. Names of the involved glycosyltransferases are given, and genes known to underlie expression of blood group antigens are given in parentheses. Blood group antigens are written in bold, as are the enzyme activities involved in P1 and P^k synthesis, the 2 antigens most important for this study (also highlighted by black frames and thicker arrows).