26 LABORATORY MOUSE 



Recessive spotting (s) ("piebald") 



I have seen indeed a gray variety with a white saddle and also a white 

 varietj 7 spotted with black. — Pallas, 1766. 



In this type (see Fig. 20), large unbroken areas of white are 

 present upon the belly, back, and face (3). There is a tend- 

 ency to form a white belt and a white face. Recessive spot- 

 ting (61) in its highest grade usually leaves two patches of 

 pigment about the ears, the rest of the coat being white. 

 This is the condition usually found in the Japanese waltzing 

 mouse (see Fig. 22) . Additional pigmented spots when present 

 are usually found upon the rump. Animals bearing but one 

 dose of the higher grades of spotting often have a small 

 belly patch of white, but are otherwise colored. It is possible 

 by systematic selection to produce strains with white faces 

 or belts (50). What has been said concerning the probable 

 immediate cause of dominant spotting (tyrosintyrosinase 

 inhibition) applies to recessive spotting as well. 



Yellow belly (A w , a 1 ) (white belly, light belly) 



The back is a gray tinged with red-brown, the belly is bordered with 

 red-brown: the exact livery of the field mouse. — Cuenot, 1907. 



It has been found in the laboratory as well as in the wild 

 state that mice may mutate (113, 136) to a yellow-bellied or 

 white-bellied condition (see Fig. 19), in which the ventral 

 hairs have an exceedingly long, light, apical band, in some 

 cases even to the exclusion of all other pigment. There is a 

 characteristically sharp demarcation on the sides and under 

 the chin, with a patch of darkly pigmented hair upon the 

 neck, shaped like a bow tie. 



This bodily distribution pattern behaves as a dominant 

 to all known color characters or their combinations, includ- 

 ing yellow, i.e. it may be associated with the general coat 

 coloration of any other type. It has been found in agouti 

 (23, 137) and non-agouti forms (lJf.6), but not in combina- 

 tion with the lethal-yellow mutation. The wild gray mouse 

 possessing this character has a normal back and a white or 

 buff belly often tinged with red-brown along the sides (A w ). 



