No. 635] 



WHITE SPOTTING IN MICE 



4*1 



breed fairly true to these different conditions. The re- 

 sults of the first mentioned matings have shown in gen- 

 eral that the altered expression of the spotting factors 

 W and s in the direction of more or less white spotting is 

 definitely transmitted to the offspring. The evidence on 

 this point is presented in Table II. 



Cross 1 of this table presents the distribution of off- 

 spring of crosses of black-eyed whites with dark pie- 

 balds, viz., those with dorsal white spotting ranging 

 from 0-10 per cent. Among the black-eyed white parents 

 all grades of spotting were approximately equally rep- 

 resented. The mode of the black-eyed white offspring is 

 at 85-81 per cent, of white, the mean of white spotting 

 is 80.5 per cent. ± .7 per cent,, and they range from 100 

 to 51 per cent, white, with a standard deviation of 11.65 

 ± .5. The piebald young have a mean grade of 10.9 ± .4 

 per cent., a standard deviation of 8.1 ± 3, and all grades 

 of piebald from to 50 per cent, white are represented, 

 although the majority is less than 20 per cent, white. 

 With these crosses are to be compared the offspring of 

 Cross 2, of which the parents were black-eyed whites of 

 the same grades as were used in Cross 1, and light pie- 

 balds, viz., those which were more than 10 per cent, white 

 dorsally. The black-eyed white young were centered 

 about a mode at 95-91 per cent, white; their mean is 

 88.5 per cent. ± .8 per cent., and their standard devia- 

 tion 7.8 ±.5. Their range is considerably less than the 

 range of black-eyed whites in cross 1, due to the absence 

 from the distribution of all classes less than 70-66 per 

 cent, white. The piebald young from Cross 2 have a 

 mean of 16.4 ± 1.2 per cent, white and a standard devia- 

 tion of 12.1 ± .8. The range of the piebalds is the same 

 as in Cross 1, but the lighter classes are more heavily 

 represented than in Cross 1, and this is reflected in the 

 higher standard deviation. 



These crosses are a test of the nature of the differ- 

 ences between darker and lighter piebalds. That such 

 differences are genetic is clearly shown by the results, for 

 the lighter piebalds have appreciably lighter offspring 



