HEREDITY 2 I 3 



Blood is always typed, if possible, before a transfusion. People of group 

 O have two substances in their blood stream known as antibodies a and b. 

 These react with antigens A- and B in such a manner as to cause clumping 

 of the red blood cells. Such a reaction is called agglutination. If a per- 

 son of group O should receive blood from any one of the other three 

 blood groups, antigen-antibody reactions would result in agglutination 

 of the red cells taken in. Likewise those of group A cannot donate to those 

 of group B and those of group B cannot donate to those of group A. 

 Those of group AB cannot donate to those of any other group. Stored 

 plasma can be given to those of any group as the red cells, which contain 

 the antigens, have been removed. 



Different races show significant variations in the percentages of the four 

 blood groups (see table below). North American whites show approxi- 

 mately the same percentages as do northern Europeans. Generally speak- 

 ing, Asiatics show higher percentages of B and less of A than do Europeans. 

 Most American Indians appear to have very low frequencies of both 

 antigens. These variations are of great interest to physical anthropologists, 

 as they serve to suggest common origins and migrations in the evolution 

 of human populations. 



Distribution of the Blood Groups Among Various Racial Groups. (After Weiner) 



Racial Group 



North American Whites 



Peru Indians 



Navajo Indians 



Arabs , . . 



Chinese , 



Natives of India 



Negroes, West Africa . . 



Negroes, U.S.A 



Russians 



Spanish 



Swedes 



The anthropoid apes have four blood groups, corresponding to those 

 in man. This suggests that the blood group mutations may have occurred 

 among the common ancestors of such apes and man. Different blood 

 antigens have been shown to be present in many mammals. In domesti- 

 cated rabbits, strangely enough, there are four blood groups whose heredi- 

 tary behavior corresponds exactly to the blood groups in man and apes. 

 Recent work shows a tremendous variation in cattle in regard to blood 

 antigens and their inheritance. 



Two other blood antigens, known as M and N, occur in man quite in- 

 dependently of the blood group antigens. The antibodies for the M and 

 N antigens do not occur in man, but are prepared from the blood of 



