84 Colours of Mice [CH. 



Wholly Coloiired and Pied Varieties. 



In the analysis of the relationship between the whole 

 or self-coloured forms and the varieties which differ from 

 them in having an admixture of white many curious and 

 specific phenomena are met with. It is probably true to 

 say that generally the whole-colour is dominant to the pied, 

 but several examples to the contrary are already known. 

 In all the cases yet studied the genetic properties of the 

 pied types can be represented factorially by regarding the 

 pattern or distribution of the colour as due to a distinct 

 factor or to its absence. Where the whole-colour is a 

 dominant, the presence of the factor must be taken as 

 causing that distribution, so that in the absence of that 

 factor the individual is pied. Conversely if the pied type is 

 dominant the presence of the pattern-factor acts by re- 

 straining the distribution of the colour, and in the absence 

 of the restraining factor the whole-colour prevails. 



One of the clearest cases is that studied by Hurst in 

 the rabbit, where the pattern known as " Dutch-marked" 

 was proved to be a recessive. In the Dutch rabbit the 

 hind quarters are coloured, for example with grey or black, 

 while the front half of the body is white except for a patch 

 of colour grey or black as the case may be surrounding 

 the eyes and covering the ears. This pattern though 

 fluctuating in minor respects is fairly definite and is at once 

 distinguishable both from the self-colours and from the 

 various other pied forms. The cross between a pure self- 

 colour and a Dutch gives F^ nearly self-colour with F z 

 consisting of 3 selfs : i Dutch in the ordinary way. An 

 interesting feature is however 10 be observed in the fact 

 that the heterozygotes between self and Dutch generally 

 (? always) have some small amount of white collar, marked 

 especially on the back behind the head. Apart from 

 Mendelian experiment it might have been supposed that 

 such a white mark showed that the aiiimal contained some 

 albino blood. Experiment shows on the contrary that the 

 actual self-colours may be carrying albino as a recessive, 

 while the small white mark is an indication of heterozygosis 

 with Dutch pattern only. 



The behaviour is in all respects as if the whole-colour 



