COLOR MUTATIONS IN MICE OF PEROMYSCUS 307 



Two skins of the white race of Peromyscus have been tested 

 with the tint-photometer. Although these pelages are probably 

 as 'white' as those of any albino mammal, they are obviously 

 not of so intense a white as the standard magnesium carbonate. 

 Few persons, however, would probably expect to find such a 

 considerable reduction in luminosity as actually occurs. The 

 percentage of white proved to be only 75.7, as compared with 

 the standard, leaving 16.7 per cent of black and 7.5 of 'color/ 

 in this case a yellow (R:G = 1.58). Neither black nor yellow, 

 however, are due to the presence of the ordinary hair pigments, 

 since these appear to be entirely lacking. The black results 

 chiefly from the loss of light which passes through and between 

 the nearly colorless hairs, and is not reflected back to the eye. 

 The proportions of the primary colors are not quite the same, 

 however, as in the standard, owing doubtless to a faintly yellowish 

 tint in the keratin of the hair. 



YELLOW-PALLID CROSSES 



Matings w^ere made between eight yellows and three pallids, 

 resulting in the birth of twenty-two young. These were all of 

 the wild type, of a medium shade, and fairly uniform in color, 

 presenting about the same appearance and range of variation 

 as a similar number of local gambeli. The yellows employed 

 were partly of the 'a' strain, partly crosses between the 'a' and 

 'b' strains. 



Of the Fi generation, 5 males and 11 females were successfully 

 mated, yielding 64 young. There thus chanced to be exactly 

 four times the minimum number required for the proportional 

 representation of all classes in a dihybrid cross. Of the 64 F2 

 individuals, 36 were males, 27 females, and one of unknown sex. 

 Since there were no significant differences in the distributions 

 of genetic classes, according to sex, males and females will be 

 combined in the treatment below. 



On the assumption that we had to do here with a typical di- 

 hybrid cross, involving complete dominance, the most probable 

 distribution of classes for this number of individuals would be: 



