COLOR MUTATIONS IN MICE OF PEROMYSCUS 301 



Independent lines of 'yellows^ 



As already stated, the presumably heterozygous male parent 

 of the 'V stram produced one yellow and four dark offspring 

 when mated with one of the nine females (P 9 91) which were 

 used in addition to the mother of the '6' yellovv'^s. There is no 

 record of any member of this brood having left any descendants, 

 the skin of the yellow was not preserved. 



Three yellows and three normals were produced by the mating 

 of a 'V yellow (Ci cf 78) with an unrelated wild-type mouse 

 (Ci 9 96), which was considerably paler than the average 

 but was not regarded as a 'yellow,' even an 'atypical' one. These 

 mice likewise left no descendants. 



Another independent outcropping of the 'yellow' mutation 

 consisted of a single individual, which appeared in a brood of 

 three, whose parents and grandparents were known to be of 

 the 'wild color.' This chanced to occur in the course of an ex- 

 periment in which paler and darker strains of the 'normal' mice 

 were crossed. We are not, however, disposed to attribute any 

 significance to the latter fact. As in the preceding cases, the 

 parents of the yellow individual were doubtless heterozygous for 

 the yellow factor, unless they were themselves producing 'mutant' 

 germ-cells de novo. This strain, likewise, was not continued 

 further. 



Yet another independent appearance of the 'yellow' color 

 variety, which we may call the 'c' strain, occurred in a lot of 

 La Jolla gambeli which are believed to have been trapped at least 

 a year later than any of the preceding ones. A pair of wild mice 

 ('selection series' P 9 118 and P d^ 22) gave rise to eight young, 

 of which three were yellows (one of these being doubtful), the 

 remainder being of the normal color type. The female was 

 likewise mated to a yellow male of the 'a-5' lot, and the male was 

 mated to three yellow females of the 'o,' '6,' and mixed strains. 

 Among the thirteen young thus produced, only three yellows 

 appeared, instead of six or seven as would be the expectation 

 from such a mating. As in the case of all of the yellows, subse- 

 quent to the 'a' and '6' strains, these lines were brought to a 



