62 MENDELISM chap, vi 



The results of two such series of gametes being 

 brought together are shown in the usual way in Fig. 

 II. A blue is a bird containing the colour factor 

 but lacking the black modifier, i.e. of the constitution 

 CCbb, or CM, and such birds as the figure shows 

 appear in the F^ generation on the average three 

 times out of sixteen. Reversion here comes about 

 in F^, when the redistribution of the factors leads to 

 the formation of zygotes containing one of the two 

 factors but not the other. 



