So we see that all three antigens have the oligosaccharide sequence in common. Now what ultimately determines if an individual has one of these three types of antigens or if they have both of these antigens? Well, basically it's the genetic information in the DNA. If the individual contains a gene that codes for a specific glycosal transferase that is able to actually form this bond, then they're going to have the A antigen. If they have that specific gene that expresses the glycosal transferase that creates this bond, then they're going to have the B antigen. If they have both genes that basically create both of these glycosyl transferases that form both of these linkages then they're going to have both of these antigens and so they're going to have the blood group AB.