No. 572] 



MULTIPLE ALL K LOM01W11S 



457 



TABLE IV 



Yellow and Chocolate 

 Yel. Choc. 



The experiment is not demonstrative, however, unless 

 both the yellow daughters and sons are bred to chocolate, 

 for it might he that yellow and agouti are linked and 

 crossing over might occur in one sex and not in the other 

 sex. For instance, if we start again with yellow by choc- 

 olate, then if their yellow offspring contain agouti linked 

 to yellow that does not cross over in one sex, let us say in 

 the males, it follows that a yellow male bred to chocolate 

 would give only yellows and chocolates, for the agouti 

 gene would go with the yellow. Therefore, both sexes 

 must be tested. This essential element in the proof has 

 been overlooked by Little, for he fails to state whether his 

 test experiments were made with both sexes. In my 

 main experiments I have used yellow sons only, and the 

 tables are based on those data, but in a few cases I have 

 mated the yellow daughters (whose brothers were agouti) 

 also to chocolate and have found that these females give 

 only yellows and chocolates, which shows for both sexes 

 that no crossing over of yellow and agouti occurs. 



A specific case will illustrate this point. A yellow 

 male was bred to a chocolate female and gave 5 yellow 

 and 7 gray offspring in two litters. One of the yellow 

 daughters was bred to chocolate and in four litters pro- 

 duced 11 yellows and 9 chocolates. A yellow grand- 

 daughter gave 9 yellows, 7 chocolates and 4 whites. 



A yellow female bred to chocolate gave 8 yellows and 

 16 chocolates, but as I have no record of the preceding 

 generation, I can not be sure that this result is compar- 

 able to the last. It shows at least that a yellow female 

 gave only two kinds of offspring. 



A "New Gray" Factor 



A word may be added about the "new gray." In the 

 original stock obtained from Mr. Horton there was a 



