No. 647] SHORTER ARTICLES AND DISCUSSION 573 



A FOURTH ALLELOMORPH IN THE ALBINO SERIES 

 IN MICEi 



In recording the occurrence of a new mutant gene in the 

 house mouse, allelomorphic to color and albinism, Detlefsen 

 ('21)2 described a very dilute, wild form in which the hair 

 showed traces of a light brownish tinge with a suggestion of 

 sootiness, and the eyes were somewhat less heavily pigmented 

 than in the wild type. This general form of pigment reduc- 

 tion is also characteristic of other color allelomorphs; for in 

 the case of the ruby-eyed rat, the ruby-eyed guinea-pig and the 

 chinchilla rabbit (Castle '21),® the yellow pigment is very 

 greatly reduced or even obliterated, while the darker pigments 

 (black or brown) are at least slightly modified. The mutant 

 mouse, however, showed a far greater pigment reduction than 

 either the rat, guinea-pig or rabbit mutants. Breeding tests 

 demonstrated that this dilute mouse mutant was a color-albino 

 allelomorph, and in this respect resembled the ruby-eyed rat 

 and guinea pig genetically (the chinchilla rabbit had not beeti 

 recorded at that time), but Dr. Detlefsen pointed out that "it 

 is hardly safe to insist that these mutations are identical. . . . 

 We are also unable to prove that they are different, for the 

 genes may be identical but simply give different somatic ef- 

 fects, since the residual inheritance can not be the same." He 

 also suggested that the discovery of a new dilute type of mouse 

 (which he was seeking at that time), more like the rat or 

 guinea pig in its somatic appearances as well as in its genetic 

 behavior, would give us more assurance that his extreme dilute 

 mouse mutant was not the homolog of the ruby-eyed rat or 

 guinea pig. Unusual as it may seem, I had discovered exactly 

 such a new dilute mutant mouse in January, 1919. By com- 

 paring it with Dr. Detlefsen 's set of rodent skins and by test- 

 ing it in appropriate matings, I recognized its genetic signifi- 

 cance just before his paper appeared in print. 



The discovery of this new mutant mouse enables us to say at 

 once that the extreme dilute mutant was not the homolog of 

 the ruby-eyed rat or guinea pig or the chinchilla rabbit, and 

 supports Dr. Detlefsen 's position in hesitating to homologize 



1 Paper No. 22 from the Genetics Laboratory, College of Agriculture, 

 Tniversity of Illinois. 



2 Detlefsen, J. A., 1921, Amer. Nat., Vol. 55, p. 469. 



3 Castle, W. E., 1921, Science, N. S., Vol. LIII, p. 387. ^ 



