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 Ccbb, 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. 



