Hh blood group final step in the synthesis of the molecule. Depending upon a person's ABO blood type, the H antigen is converted into either the A antigen, B antigen, or both. If a person has group O blood, the H antigen remains unmodified. Therefore, the H antigen is present more in blood type O and less in blood type AB. Two regions of the genome encode two enzymes with very similar substrate specificities: the H locus (FUT1) which encodes the Fucosyl transferase and the Se locus (FUT2) that instead indirectly encodes a soluble form of the H antigen, which is found in
Blood type pregnancy or occasionally a blood transfusion with D positive RBCs. Rh disease can develop in these cases. Rh negative blood types are much less common in Asian populations (0.3%) than they are in European populations (15%). The presence or absence of the Rh(D) antigen is signified by the + or − sign, so that, for example, the A− group is ABO type A and does not have the Rh (D) antigen. As with many other genetic traits, the distribution of ABO and Rh blood groups varies significantly between populations. 28 blood-group systems have been identified by the International Society for