"DOMINANT" AND "RECESSIVE" SPOTTING IN 

 MICE 



C. C. LITTLE, 

 Bussey Institution. Harvard University 



Introductory 

 The inheritance of spotting lias long- proved of interest 

 to animal geneticists. The nature of spotting is such 

 as to afford an excellent chance to observe quantitative 

 fluctuation and variations of very minute size. Further- 

 more, the fact that spotted varieties are found in all the 

 rapidly breeding smaller domesticated mammals has led 

 to a widespread investigation of its phenomena of in- 

 heritance. 



One of the most clean-cut and constant types of spot- 

 ting which has been studied is that of the "hooded" pat- 

 tern in rats. This character was studied independently 

 by Doncaster (1905) and by Castle and McCurdy (1907). 

 All these observers agree that this form of spotting is 

 due to a recessive Mendelizing unit which gives a 1:3 

 ratio in crosses with self-colored races. 



In mice there has been no such well-localized pattern 

 recorded and a series of spotted forms has been described 

 which vary from black-eyed whites on one end of the 

 series to heavily colored animals having only a few 

 white hairs on the forehead or on the belly at the other 

 extreme. 



Cuenot, who did considerable work on the inheritance 

 of spotting in mice, came to the conclusion that spotting 

 is due to a group of recessive spotting factors which he 

 describes as pi, p2, p3, p4, etc. His figures, however, 

 show a single unit character difference as 3:1 and 1:1 

 ratios prove. 



Up to 1908 all the spotting in mice was classed as re- 

 cessive to solid-colored coat. At that time, however, 

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