SCOPE OF GENETICS 27 



prising that there is sometimes an interaction 

 between factors that have quite distinct roles 

 to perform. These interactions are probably 

 of several kinds. One, which I shall illus- 

 trate presently, is probably to be represented 

 as a repulsion between two factors. As a 

 consequence of its operations when the 

 various factors are sorted out into the gametes, 

 if the individual be cross-bred in respect of 

 the two repelling factors, having received so 

 to speak only a single dose of each, then the 

 gametes are made up in such a way that each 

 takes one or other of the two repelling factors, 

 not both. 



Mutual repulsions of this kind probably 

 play a significant part in the phenomena of 

 heredity. A single concrete case which Mr 

 Punnett and I have been investigating for 

 some years will illustrate several of these 

 principles. We crossed together a pure 



