2 14 READINGS IN BIOLOGICAL SCIENCE 



rabbits. The M and N blood types are of no consequence in transfusions. 

 They are used in the same manner as the blood group antigens in cases 

 of disputed parentage. Only two genes are involved in the M and N types. 

 One results in the formation of antigen M and the other in the formation 

 of antigen N. Like the blood group antigens, M and N show no dominance 

 with respect to each other. Unlike the blood groups, however, everyone 

 possesses two genes for the production of antigens. No individuals have 

 ever been found corresponding to blood group O, that is, lacking both 

 M and N antigens. People are of three genotypes; homozygous for antigen 

 M, homozygous for antigen N, and heterozygous for antigens M and N. 

 There is only one genotype for each of the three phenotypes. The table 

 below illustrates how both the blood groups and the M and N types may 

 be of value in cases of disputed parentage. 



Examples of How the Blood Groups and Types may be Used in the Determination 



OF Paternity 



Lines in columns 5 and 6 signify that the father could belong to any group or type. 



As the M and N types are independent of the blood groups, it is pos- 

 sible by testing for both blood reactions to greatly increase the efficiency 

 of tests for disputed paternity. Twelve combinations of blood groups and 

 types are possible within individuals. 



Significant racial variations are manifested in the occurrence of the M 

 and N types although they are less marked than in the blood groups (see 

 table below). The knowledge and techniques of the M and N types are 

 more recent than for the blood groups, and the available data are cor- 

 respondingly less extensive. 



No other hereditary traits in man have as yet been discovered which 

 are as universally satisfactory to work with as are the blood groups and 

 types. They are established before birth and remain constant throughout 

 hfe. The tests for them are objective and clearcut, much more so than 

 for P.T.C. Moreover they show considerable variability and none of the 

 genes involved are rare. 



Boyd recently tested the blood groups of over one hundred Egyptian 

 mummies. His findings indicate that the distribution of the blood groups 

 among the ancient Egyptians five thousand years ago was apparently 

 about the same as among modern Egyptians. 



