Xo. 632] SABLE VARIETIES OF MICE 



the blacks derived from these varieties. Sooty, then, ap- 

 pears to be a lower stage of sable in the more complete 

 restriction of non-yellow pigments from the hair. 



In addition to the varieties treated above it is neces- 

 sary to speak of light bellied mice which can not be in- 

 cluded in the sable series. I refer to the light-bellied 

 agouti variants reported by Cuenot and Morgan. These 

 variations have been shown to belong to a series of mul- 

 tiple allelomorphs in which the other members are ordi- 

 nary agouti, yellow, and non-agouti. The light-bellied 

 agouti also arose spontaneously in Little's 1916 crosses 

 between gray-bellied agouti and dilute brown. Such 

 light-bellied agoutis bred true and when crossed with a 

 non-agouti variety they produced in F 2 only light-bellied 

 agoutis and normal non-agoutis. This result contrasts 

 strongly with the result of a cross of black-and-tan with 

 wild agouti which produces only sables and gray-bellied 

 agoutis in F x , while in F 2 there result yellows, sooties, 

 sables, black-and-tans, agoutis and darkened agoutis. 

 The difference is readily seen to be due to the yellow 

 gamete of the sable series. 



To explain the results of the genetic behavior of sables 

 one is led to review the origin of the varieties concerned. 

 The wild house mouse is undoubtedly the ancestral type 

 from which all varieties of fancy mice have descended. 

 Its pelage contains the three fundamental pigments of 

 mice: yellow, black and brown, formed in the mosaic 

 known as the agouti pattern by the presence of a specific 

 gene "A." Each pigment is likewise determined by a 

 gene, Y for yellow, B for black, b for brown (absence of 

 black) and by loss of one or more of these genes, or by the 

 gain of other genes determining the distribution of the 

 pigments present, the whole array of fancy varieties has 

 resulted. 



Yellow was shown by Cuenot to be due to a change in 

 the gene "A," resulting in the presence of a restrictive 

 factor which limits the distribution and amount of black 

 and brown pigment, the eyes alone being dark pigmented 

 while black or brown pigments are present in the hair and 



