306 GENETICS 



the black pigment hides all the others, so that the coat color 

 is solid black. Other changes are made by altering the genes 

 C or D. There were thus five varieties differing in color 

 from the wild type. The different varieties had the follow- 

 ing constitution, so far as these five pairs of genes are con- 

 cerned. 



The wild-type (brownish-gray) is: 



ABCDG 

 ABCDG 



The five varieties each due to modification of one wild- 

 type gene pair are: 



When any two of these five varieties are crossed, they 

 produce in Fi the wild type, since each contains a dominant 

 gene corresponding to the recessive gene of the other. Thus 

 by crossing number 3 with number 5 we obtain 



ABcDG 

 ABCDg 



And since this contains a dominant gene in every pair, 

 these show the brownish-gray, wild-type color. But when 

 these Fi individuals are mated together, we are dealing 

 with individuals that are heterozygotic for two pairs of 

 genes Cc and Gg. Such individuals, as we saw on page 117, 



