HEREDITY 



produces the three kinds of young, agouti, black, 

 and red; the second sort produces only agouti 

 young and red young ; the third sort produces 

 only agouti young and black young. The fourth 

 sort produces only agouti young, i. e. repre- 

 sents the fully fixed agouti type, the completely 

 recovered wild type. 



In the chart (Fig. 35) are indicated cer- 

 tain gametic unions which would lead to the 

 production of these four classes of agoutis. 

 The probable frequencies of their occurrence 

 on the basis of chance are 4:2:2:1. 



Experiment made it clear that R as an inde- 

 pendent gametic factor is not necessary to the 

 production of the agouti character, as was at 

 first thought to be the case, but that any 

 gametic union which includes both B and A 

 will produce an agouti individual whether 

 R is or is not present. Yet a microscopic 

 examination of the agouti hair shows that 

 red pigment is present in a distinct band 

 near the hair-tip. As a matter of fact all 

 black individuals, even when they breed true, 

 probably form some red pigment along with 

 the black, but its presence is overlooked when 



68 



