No. 555] SIMPLIFICATION OF MENDELIAN FORMULAE 177 



dominant or recessive character is indicated by the sym- 

 bol, whether large or small. For example, consider the 

 mouse-color series as described by Castle and Little 

 (1909). In the paper cited, nine color factors were de- 

 scribed, three of which clearly recessive have already been 

 mentioned, viz., d, p and s. The remaining six were con- 

 sidered dominant factors. Mr. Little has since suggested, 

 and I think with good reason, that one of them had 

 better be omitted, since its existence has not been demon- 

 strated beyond question. The six as given were C, the 

 color factor ; Y, the yellow factor ; Br, the brown factor ; 

 B, the black factor; R, the restriction factor (producing a 

 yellow coat) ; and A, the agouti or gray factor. 



Mr. Little would omit either C or Y, since it has not 

 been shown beyond question that the effects which had 

 previously been ascribed to these two are not due to one 

 and the same agency. 



With the eight symbols which would remain, three being 

 small letters, the others being or beginning with capitals, 

 it is possible to write, without duplication of terms, for- 

 mulas descriptive of the entire color series. But in so 

 doing it would be necessary to designate the original or 

 wild form in terms of factors supposed to be lost in its 

 derivatives, and which have only come to light through 

 such loss. This, as Morgan points out, involves rede- 

 scribing the wild form every time a mutation arises and 

 should be avoided if possible. I therefore favor Morgan's 

 suggestion that each mutation as it arises be given some 

 suitable descriptive name, the initial or other significant 

 letter of which shall be its symbol. If, as is commonly 

 true, the mutation is recessive in crosses with the wild or 

 original type, its symbol will be a small letter. But if the 

 mutation is dominant, 8 its symbol should be a large letter. 



The original or wild type need not be described in terms 

 of its mutations, as every duplicate system of termin- 

 ology, even Morgan's, requires. The system would ac- 



one in mice, so that they can scarcely be called rare. 



