260 



Biology in America 



in very small flecks. If two blue Andalusians are crossed 

 they produce one black, two blue, and one white splashed 

 with black ; while when the first and last of these offspring 

 are interbred, only "blue" fowls result — a Mendelian pro- 

 ceeding, which is strictly "according to Hoyle." Here we 

 have two factors, black and white, which instead of blending 

 in the cross enter into it unmodified, but distributed in such 

 a way as to produce a result different from that of either 

 parent. Furthermore, the ' ' recessives ' ' Tiere carry a little 

 of the "dominant" factor in the splashes of black on a white 

 background. 



Inheritance of Ear Length in Eabbits 

 Figs. A and B, parents; C and D, offspring of the first and second 

 generations, respectively, with ear lengths intermediate between those 

 of the parents. From Castle, "Genetics and Eugenics." 

 By permission of Harvard University Press. 



A closely similar case is that of red and white cattle, which, 

 when interbred, produce "roan" offspring, these latter in 

 their turn "throwing" red, roan and white in the proportion 

 of 1:2:1. 



In some cases of supposedly complete dominance careful 

 measurements show that the dominant factor is slightly modi- 

 fied by the recessive. Thus when wild fruit flies are crossed 

 with those having small wings, the long wings of the for- 

 mer dominate the short wings of the latter ; but not com- 

 pletely, for the wings of the hybrid average slightly less 

 than those of the wild parent. And this gives rise to the ques- 

 tion whether dominance is ever perfect, even in those cases in 



