BLOOD GROUPS 53 



as those of individuals of genotype AA. The same holds for BB 

 and BO. Consequently, we have to classify both AA and AO as 

 group A, and BB and BO as group B, giving the four Landsteiner 

 blood groups, as shown in Table 4-2. 



TABLE 4-2 



Genetically Determined Types (Genotypes) and Serologically Determined Types 

 (Blood Groups) 



Approximate percentage of 

 Genotype Blood group U.S.A. population 



00 O 45 



aaI 



AOl 



bb| 



BOj 



AB AB 3 



A 42 



B 10 



It was soon found that there were two kinds of A antigen. The 

 more common one, and in Asian populations the only one present, 

 reacts strongly with anti-A agglutinins and is designated as Ai. The 

 other, confined to Europeans and Africans and their descendents 

 in other parts of the world, often reacts weakly with anti-A and is 

 called A2. This distinction enables us to divide the population of 

 Europe and Africa into six blood groups instead of four, as follows : 

 O, Ai, A2, B, AiB, and A2B. The difference seems to be of little 

 importance for transfusion but is interesting to anthropologists and 

 students of legal medicine. 



Althotigh in Table 4-1 group O erythrocytes are shown as having 

 no antigen, this is not strictly true. They possess antigens connected 

 with other blood group systems still to be discussed and also have 

 an antigen connected with the ABO blood group system. Human 

 plasma does not ordinarily contain an agglutinin for this antigen, 

 but the plasma of individuals of the subgroup AiB and the normal 

 serum of certain animals may contain one. The agglutinin can be 

 found in the serum of certain eels, apparently more regularly in the 

 European than the American eel, and may be produced by immuniz- 

 ing a goat with SJiiga bacilli. None of these sources is always availa- 

 ble, nor is the agglutinin so obtained always strong and reliable. It 



