COLOR MUTATIONS IN MICE OF PEROMYSCUS 



299 



the parents in their mean color tone, though they presented a 

 considerable range of variability. A single mating between a 

 '6' male and a heterozygous 'a' female led to the birth of one 

 offspring of the wild color and two decidedly 'atypical' yellows. 

 It is thus evident that these two shades of yellow do not result 

 from the modification of independent genetic factors, as is the 

 case with the other color mutations to be described presently. 

 Assuming that the differences between the 'a' and 'b' strains are 

 hereditary at all — which seems fairly certain — we may, on the 

 one hand, have to do with a case of 'multiple allelomorphs,' 

 the two 'yellows' representing slightly differing modifications 



TABLE 3 

 ' B' yelloivs 



of the same color factor. Or the primary factor concerned may 

 be the same in the two cases, the difTerence being due to the 

 presence in one variety of a secondary 'modifying' factor. 



The mature pelages of twelve of these hybrid yellows were 

 subjected to the color analysis. The mean values for black, 

 white, and total 'color' are close to those for the two 'pure' 

 strains, which, as stated before, agree closely with one another 

 in these respects. Furthermore, these hybrids are strictly in- 

 termediate as regards the spectral position of their yellow pig- 

 ment, as is indicated by the ratio of red to green. This is true 

 not only of the mean value of this ratio (3.33), but of its range. 

 As already stated, this intermediate ''condition is apparent to 

 the eye. 



