The Rhesus Blood Groups 



291 



the N type is NN, and the MN type is MN. The various pos- 

 sible crosses among these types with the genotypes of the parents 

 and ratios in the offspring are illustrated in Table 13. A study 

 of this table shows that neither the M nor the N agglutinogen 

 can be present in the blood of a child unless it was also present 

 in the blood of one or both parents. It shows also that an indi- 

 vidual of type M cannot give rise to a child of type N, since 

 type N would be homozygous for gene N, and that a type N 



TABLE 13 



Results of Crosses between Various Genotypes Producing the MN 



Blood Types 



The results of reciprocal crosses are the same, 

 are not considered here. 



The subtypes of type N 



person cannot produce a child whose blood belongs to type M, 

 since type M would be homozygous for gene M. Such relation- 

 ships are taken into account when these blood groups are used 

 as tests of dubious parentage. These M, N, and MN types, 

 however, do not usually interfere with blood transfusions because 

 human serum does not normally contain the agglutinins which 

 would cause the blood to be agglutinated. 



The Rhesus Blood Groups 



An extensive series of studies by Wiener, Levine, Race, Taylor, 

 and others have shown that another series of antigens is also 

 present in human beings. The presence of such antigens was 

 revealed independently by Levine and Stetson and by Land- 

 steiner and Wiener. The latter two investigators showed that 



