The terminology is very confusing: P1 is part of the P blood group and is not part of the globoside blood group (P, Pk). Some of the same enzymes act on both substrates, leading to even more confusing names. The pp phenotype is the result of a defective gene acting on both the P and globoside blood group. The reason I include this lecture is that the “p” phenotype is seen in the Middle East region and produces an antibody anti-PP1Pk (anti-Tja) and is one of our antibodies to a high incidence/prevalence antigen.