THE OCCURRENCE OF THREE RECOGNIZED 

 COLOR MUTATIONS IN MICE 



Dr. C. C. LITTLE 

 Harvard Medical School 



The common wild mouse, Mus musculus, has a type of 

 coat-color pattern well known to geneticists as being 

 characteristic of almost all wild species of rodents. This 

 pattern is commonly called the "agouti" pattern. It 

 consists in a "ticking" or "banding" of the hairs of both 

 dorsal and ventral surfaces. On the dorsal surface each 

 hair has a subapical band containing yellow pigment. 

 The tip of the hair is black pigmented, while the half 

 proximal to the yellow band is dark, containing both 

 black and brown pigment granules. The general effect 

 of the dorsal surface, when considered as a whole, is dull, 

 brownish gray. The ventral surface is distinctly duller 

 and paler than the dorsal. The distal half of the hair is 

 lightly pigmented with black and occasionally with some 

 yellow pigment, while the proximal half is much more 

 heavily pigmented with black and brown granules. The 

 general impression, conveyed by the ventral surface, is 

 dull faded gray. This fact has led to the adoption by 

 various investigators of the term "gray-bellied agouti" 

 to describe the wild mouse color pattern. 



In addition to this gray-bellied agouti another type of 

 agouti house mouse has been reported as occurring wild 

 in certain localities. This type has been used in genetic 

 investigations by Cuenot and by Morgan. 1 



The chief difference between the gray-bellied agouti and 

 the aberrant type is that the latter has, generally speaking, 

 more yellow and brown and less black pigment. This is 

 especially true of a band of hairs which runs laterally along 



1 Morgan, noticing that Cuenot 's mice of this variety had a small patch 

 of reddish brown hair between the front legs while his own mice had not, 

 has suggested the possibility that the variety with which he worked was 



this color variety with and without the spot and therefore hope soon to 



