286 



Blood Groups 



people do not possess the alpha agglutinin or antibody. If, 

 however, it is injected into group or group B individuals, they 

 may die because they possess the alpha agglutinin and their red 

 corpuscles will be clumped together into small masses which 

 block the circulation of the blood. In a similar way, blood from 

 persons of group B can safely be introduced into people of 

 groups B and AB but not into individuals of groups or A. 

 Blood from group can be introduced with reasonable safety 

 into people of types A, B, and AB because it does not contain 

 the A or B agglutinogen (antigen) and therefore will not be 

 agglutinated by A, B, or AB types of blood serum. Finally, 

 blood from people of group AB can be introduced only into 

 people of the same group. Such persons have both the A and 

 B agglutinogens (antigens) ; therefore their blood will be ag- 

 glutinated by any blood that has either or both of the agglu- 

 tinins (antibodies). The four groups with their respective geno- 

 types, agglutinogens, and agglutinins, and the various agglutina- 

 tion reactions are summarized in Table 11. 



TABLE 11 

 The Landsteiner Blood Groups and Some of Their Properties 



The question of blood groups is interesting genetically be- 

 cause it is another case of multiple alleles. Its practical nature 

 is very important, however, for the blood-group reaction not 

 only determines what transfusions can and cannot be made with 

 safety but also has been used in several legal cases where the 

 question of dubious parentage is involved. Sometimes it can 

 be shown definitely that a child cannot be of a certain putative 

 parentage because a cross between two individuals of certain 

 blood groups cannot produce certain other blood groups. If a 



