VII] Colours of Thorough-bred Horses 123 



Thus the gametes for each of the four non-yellow colours 

 are as follows : 



Agouti (with black) G,B . Ck. 



Cinnamon agouti (without black) G .5 . C/i. 



Black g ' ^ ' Ch, 



Chocolate g - ^ - Cli. 



Yellows being ahvays heterozygous, all zygotes con- 

 taining yellow are to be represented by adding Yy to the 

 zygotic formula produced by compounding two of the above 

 gametic formulae. Thus the yellows which throw chocolate 

 only are 



Yy . gg . bb . CJiCh. 



The yellows throwing black only are 



Yy . gg . BB . ChCh, 



and so on. This representation must in any case approxi- 

 mate to the truth, but there is still some doubt whether the 

 relation of yellow to non-yellow is quite so simple as here 

 suggested"^. 



We now pass to two cases which are of some interest 

 on account of the somewhat conspicuous part that they 

 have played in general discussions of heredity. The first 

 is that of Race horses, where the phenomena, in so far as 

 they have been adequately studied, are remarkably simple. 

 The second example, that of the Basset Hounds, presents a 

 feature of complexity. 



Race Horses. 



In '* thorough-bred*' or race horses the behaviour of the 

 yellow and black pigments In descent is comparatively 

 simple and the facts thus form a remarkable contrast with 



* Attention should be called to the fact that if the two kinds of agoutis 

 in the mouse might be supposed to represent the two kinds of yellow in 

 the rabbit then yellow of the rabbit might be sui)posed to correspond with 

 chocolate of the mouse. This natural suggestion is however negatived by 

 the fact that a definite chocolate pigment can be seen in the hairs of 

 rabbits. In the pink-eyed Himalayan rabbit the pigment according to 

 Miss Durham is exclusively chocolate. 



