The A-B Blood Groups in Human Beings 287 



group and a group A person are mated, the cross must be 

 either 00 X AA or 00 X -^O. The offspring could be only group 

 A (AO) in the former case or group A (AO) or (00) in the 

 latter. If the child is of group B or group AB, courts will admit 

 the blood group relationships as evidence that such a child could 

 not be the child of those parents. Blood groups will not estab- 

 lish parentage but will show sometimes that the supposed parent- 

 age could not he the correct one. Various combinations of geno- 

 types with the possible offspring they could produce are shown 

 in Table 12. 



Some recent studies indicate that both group A and group AB 

 are composed of two or more subgroups. Earlier results had 

 indicated that when group A blood was mixed with group B 

 serum, the serum was absorbed by the group A blood until it 

 no longer could agglutinate group A blood. This reaction was 

 to be expected since group A blood contained agglutinogen A 

 whereas group B serum contained group A agglutinin. In some 

 tests, however, when the blood of some individuals of group A 

 was used to absorb the group B serum, the serum lost the power 

 of agglutinating the blood of these individuals but could ag- 

 glutinate the blood of most other individuals of group A. This 

 seemed to indicate that there were two varieties of group A 

 blood, designated by Landsteiner and Levine Ai and Ao. The 

 agglutinogens found in these subgroups are designated as agglu- 

 tinogens Ai and A2, and the genes which determine their pres- 

 ence may be designated A-^ and Ao or 7-^^ and I^^ (theory of 

 Thomsen et al.). Since two agglutinogens determine the two 

 subgroups of group Ai, one could expect to find similar sub- 

 groups of group AB. Such subgroups have been found and are 

 designated AiB and A2B. 



It has been found, also, that the anti-A or a agglutinin also is 

 composed of several subtypes. Anti-A or a agglutinin reacts 

 with both the Ai and A2 agglutinogens, and the reaction is some- 

 what less intense with A2. Agglutinin anti-Ai or ai, on the 

 other hand, reacts strongly with agglutinogen Ai but only very 

 feebly with agglutinogen Ao. Group B and group O usually 

 contain both the a and the ai agglutinins, but this latter 

 ai may also be present in rare cases as an irregular agglutinin 

 in A2 or AoB blood. Very rarely, sera from Ai or AiB bloods 



