COLOR MUTATIONS IN MICE OF PEROMYSCUS 313 



other hand, the amount of yellow pigment has certainly been 

 increased, so that there has been a partial compensation for 

 the loss of dark pigment. The eyes, ears, and feet of the yel- 

 lows are as dark as those of the normal. 



8. These three mutant types are all recessive to the wild 

 type. The albinos and pallids breed true and exhibit compara- 

 tively little variability. Likewise they segregate clearly in 

 crosses with the wild type or with one another. The yellows, 

 on the other hand, exliibit a wide range of variabihty, intermedi- 

 ates being found between the typical yellow and the normal 

 condition. They also display other irregularities which will be 

 discussed in another section. 



9. These three mutations relate to quite distinct genetic 

 factors. Any two, when crossed, give rise to the wild type in 

 the Fi generation. In the F2 the wild type and two mutant 

 types segregate clearly, except for certain irregularities with re- 

 spect to the yellows. 



10. Albino-palhd crosses reveal the existence of a high degree 

 of linkage between these two factors. On the contrary, no link- 

 age appears to exist between the albino and the yellow factors. 

 The yellow-palhd cross was not tested in this respect. 



11. In the F2 generation of the yellow-pallid cross, the propor- 

 tion of yellows proved to be considerably too small, though these 

 discrepancies may perhaps be accidental. There were, in addi- 

 tion to the true 'yellows,' about an equal number of 'doubtful' 

 individuals, approaching the normal in appearance, which ap- 

 peared to be genetically neither true yellows nor true normals. 

 Likewise, in the original yellow cultures, there occurred, as 

 stated above, many somewhat intermediate individuals, these 

 being sometimes found in the same brood with typical ones. The 

 genetic status of these 'atypical yellows' and other 'doubtful' 

 individuals of the same stock has not yet been determined by us. 

 We are certain, however, that they are not merely mice which 

 are heterozygous for the yellow factor. Heterozygotes are 

 commonly as dark as the 'wild' type of gambeli. 



12. The 'pallid' mice, though far more regular in their genetic 

 behavior than the yellows, nevertheless show a quite evident 



