26 PHYSICAL BASIS OF HEREDITY 



but white descendants, and the F2 reds never anything 

 but red descendants. 



In this case the color of the F^ flowers is obviously 

 somewhere between red and white. In so far as the F^ 

 flower is colored, it may be said that red is dominant ; in 

 which case the red and the pink F2 classes (1 + 2 = 3) 

 are to be counted together as contrasted with the white, 

 giving a 3 : 1 ratio. On the other hand, if one chose to 

 emphasize the fact that the F^ pink flower is not red, but 

 affected by the white-producing element in its make-up, 

 then not red, but white, might be said to be the dominating 

 character ; in which case the white and the pink F2 classes 

 (1 + 2 = 3) would be counted together as contrasted with 

 the red giving an inverse 3 : 1 ratio. It appears then 

 largely a matter of choice as to what is to be called 

 dominance (see below). The essential fact of segrega- 

 tion is not affected by the decision, and it is this that is 

 fundamentally important. 



Another example of failure of complete dominance is 

 shown in the race of Andalusian fowls. In this race there 

 are blue, splashed-white, and black birds ; the blue birds 

 going under the name of Andalusians. When splashed- 

 white is mated to black, all the offspring (F-^) are blue 

 (Fig. 3) ; when these blues are bred together they give 

 1 splashed-white : 2 blues : 1 black. Evidently the blue 

 birds are the heterozygous type. Their feathers show 

 under the microscope less black pigment, somewhat dif- 

 ferently distributed from that in the black birds. The 

 intermediate blue color is due in this case to the less dense 

 distribution of the pigment in the heterozygote. Lippin- 

 cott, who has recently examined this cross in greater detail 

 than heretofore, states that the colored areas or splashes 

 in the white males are either blue or blackish according 

 to the part of the body on which they occur, and that this 

 corresponds with the distribution of the color on the Anda- 

 lusian, for while the latter is said to be blue, this applies 



