96 ANNALS NEW YORK ACADEMY OF SCIENCES 



of the experiment has not yielded as extensive results as I had hoped for. 

 In conformity with the statement of Cuenot, I found that when the 

 spotted mice (waltzers) were crossed with races having a uniform coat all 

 the mice in the first generation were uniform. In the second generation 

 (F 2 ) both uniform and spotted coats appeared, the former in excess. 

 Cuenot gave the usual Mendelian ratio 3 : 1 for this generation. I have 

 found difficulty in deciding how to classify the spotted mice, for they 

 range from those spotted like the original waltzers to those with only a 

 few white hairs on the belly or even at the tip of the tail. It is apparent 

 that, if the original coat characteristic of the spotted waltzers be taken as 

 the recessive character, this particular coat or its equivalent in spottedness 

 reappears in much less than one fourth of the second generation. I chose 

 a race of waltzers obtained from Prof. R. M. Yerkes that had a known 

 history. This race has not, it is true, a fixed spotted pattern, but within 

 certain limits the amount of white to black is fairly constant. In marked 

 contrast to this condition is the series of forms in the F 2 generation that 

 range, as stated, from the uniform coat to the original spotted condition. 

 It is perfectly evident that, as a result of crossing, the uniform coat has 

 encroached on the spotted coat, so that the latter now has a far greater 

 range in one direction than before. In a word, the spotted coat in the F 2 

 generation more often approaches the uniform coat than does the original 

 race. It is clear therefore to my mind that the relation of spotted coat to 

 uniform is far more complicated than the Mendelian ratio requires and 

 that hybridizing introduces a new factor or modifies the old one. The 

 spotted coat may in fact be said to have been contaminated by the cross, 

 so that in most cases segregation, if the process can be said in fact to be 

 one of segregation, is less complete than before. 



The problem of the spotted coat is one that has not been clearly brought 

 into line with other interpretations applied to Mendelian inheritance in 

 mice. For instance, if, as Cuenot has suggested, the albino condition is 

 due to the loss of a color producer (C), then this factor must be absent 

 from the white regions of the spotted skin, yet the factor must be present 

 in other parts of the body of the same spotted animal that produces color. 

 Hence both the color producer and the color determiner must have been 

 present in the fertilized egg. It does not seem to me to render the diffi- 

 culty any less by introducing a spotting factor, unless its mode of action 

 can be made to conform to the physiological action involved to explain 

 the presence or the absence of color in other races, for there can be little 

 doubt that the physiological process that produces yellow, gray, black or 

 chocolate spots is the same as that producing the same colors in the 

 uniform coat. On the other hand, it is evident that spotted mice are 



