8 SOME POSSIBLE BEARINGS OF GENETICS ON PATHOLOGY 



recessive when bred to the type. This is not the case. The 

 hybrid (or heterozygote) is frequently intermediate. In fact, 

 it might be said, almost without exaggeration, that the heterozy- 

 gote nearly always shows some traces of its double origin. Some- 

 times the hvbrid character is nearly midway between the parent 



B 





DIES 



Fig. 4. Yellow mouse (YB) crossed to yellow mouse (YB) produces 

 here black and yellow offspring, in the ratio of 2:1. These yellow are 

 again hybrid, and if bred to each other give the same result again. Pure yel- 

 low (YY) offspring die at early stage. They constitute one quarter of all 

 the offspring. 



types, sometimes more like one, or like the other. The impor- 

 tant fact, however, is that in the germ cell of such intermediate 

 hybrids, there is the same clean separation of the parental genes. 

 In consequence, we find in the second generation the two grand- 

 parental types in pure form and an array of intermediates con- 

 necting them. 



