vii] Peculiarities of Yellow Types 121 



Bantams, and Leghorns. It is said never to breed true, 

 throwing ordinary black-reds in unascertained proportions. 

 Presumably pile is a heterozygous combination, black-red 

 being one of the constituents, but what the other pure form 

 (or forms) involved may be, is quite uncertain. The whole 

 question is still very obscure, and from preliminary experi- 

 ments made by Mr C. Fryer it seems probable that two 

 pairs of factors are concerned in addition to black-red. 



For exhibition purposes piles are often crossed with 

 black-reds, fanciers being under the impression that a 

 brighter pile results from this mating. The fact suggests 

 that there may be piles of several different compositions. 

 Taking the known facts together the one clear deduction 

 is that pile, or yellow if we may so call it, is dominant to 

 black-red '^. 



Recapitulation and Discussion of the Foregoing 



Facts. 



The outstanding peculiarities of this group of pheno- 

 mena are as follows : 



I. The difference between the genetics of similar 

 colours in allied forms. 



In rabbits black is epistatic to yellow, giving (in the 

 absence of G, the agouti factor) simply a black heterozygote. 

 In guinea-pigs (where red represents yellow), the hetero- 

 zygote of black and red is a patch-work, viz. tortoise-shell. 

 In both rabbits and guinea-pigs when G is present this 

 heterozygote is agouti, the factor G being introduced by 

 the yellow parent. 



In mice yellow is epistatic to black, giving, in the 

 absence of G, a yellow heterozygote. We can form no 

 surmise as to the nature and causation of this discrepancy 

 between these types. It is to be observed that the recessive 

 yellow of the rabbit, viz. the blue-bellied type lacking both 

 G and B, nevertheless has some black pigment in it^blue 

 fur, while the yellow mouse does not necessarily have any. 



* The whole-coloured buff of Cochins and some other breeds derived 

 from them is quite distinct from pile. The genetics of this pigmentation 

 are complex and little known as yet. 



