912 



THE HEREDITY OF THE BLOOD GROUPS 



THE MENDELIAN MECHANISM 



It is clear that not the groups as such are inherited but the presence or absence of 

 the agglutinogens A and B. The problem becomes now: Is it possible to describe a 

 simple Mendelian mechanism that will fit the observed facts? 



Von Dungern and Hirschfeld noticed that the heredity of the agglutinogen-agglu- 

 tinin set A and a (and likewise that of the separately considered B and /3) was similar 

 to that described by Mendel in his first experiments with peas. In the language of 



TABLE III 



Genetic Formulas of the Four Groups 



Group 



Mendelism, the serological elements A and a are represented in the chromosomes by 

 two allelomorphic genes A and a, respectively, of which A is the dominant and a the 

 recessive. In a similar manner, the agglutinogen-agglutinin set B and /3 are repre- 



TABLE IV 



sen ted by the genes B and b, of which B is the dominant. Group O without any ag- 

 glutinogens is thus genetically represented by the double recessive, aabb. Group A 

 with agglutinogen A and agglutinin a is genetically either AAbb (homozygous) or 

 Aabb (heterozygous). All the genetical possibilities, according to the two-factor the- 

 ory of von Dungern and Hirschfeld, may be represented as shown in Table III. 



It is a simple exercise in genetics to calculate the groups of the children expected 

 from all the possible crosses. This has been done in detail by Ottenberg.' The sum- 

 mary of all possibilities (on the theory of von Dungern and Hirschfeld) is given in 

 Table IV. 



A great deal of attention has been paid to the medico-legal application of the 

 knowledge of the heredity of the blood groups. Reference to Table IV will show the 



» Ottenberg, R.: /. Immunol., 6, 363. 1921, 



