No. 635] WHITE SPOTTING IN MICE 493 



about 10 per cent, or less white dorsally, while those with 

 larger percentage of white are much rarer than among 

 piebalds lacking the darkening modifiers. 



3. The genotype 8s ordinarily produces the self coat, 

 but in the presence of an additional modifying gene pro- 

 duces a small amount of white spotting on the ventral 

 surface, varying in Bize from a few white hairs to 12 per 

 cent, of that surface. 



MoiMi iF.ns Ai'fectixc Localization of White Spotting 

 in Piebald Mice 



The presence of separate genes for certain localiza- 

 tions of spotting in piebald mice has been suspected for 

 some time. Fanciers, for instance, have given separate 

 names to such types as "Dutch belted" mice and have 

 claimed that they bred true to this condition, which re- 

 sembles the Dutch belted pattern of cattle. Consequently 

 when piebald mice showing distinct localization of white 

 spotting in the pelt have been born in these experiments 

 they have been saved for further study. 



The most striking of these localized spotting types 

 has appeared sporadically in the piebald stock. From 

 its appearance I have called it "white face" although 

 it varies from a small blaze of white on the forehead to 

 a white spot which covers the whole head back as far as 

 the ears. The belly is spotted with white as in ordinary 

 piebalds. The strain of wdiite face which has been iso- 

 lated breeds true to this condition, 8 matings of white- 

 face by white face having produced 46 young, all of them 

 white faced. The offspring of one pair of white faced 

 mice which were brother and sister, have been inbred, 

 brother to sister, for four generations and there have 

 been born in these matings to date 36 young, all white 

 faced, and varying but little in the amount and distribu- 

 tion of the white spotting on the face. 



One other sub-type of piebald is perhaps also sep- 

 arable. This is the type known as belted. It varies 



