492 



THE AMEBIC AN NATURALIST [Vol. XL VI 



relation is such that the characters involved fail to pass into the 

 same gamete even though they may be present together in the 

 parent zygote. That yellow and agouti in mice are not in gen- 

 eral so related is shown conclusively by experiments which will 

 be more fully described elsewhere, but which may be briefly 

 summarized in the following table : 





Parents 





Mating 



Both Yellow 











185 



397 

 273 

 159 



500 



894X895 

 502.2.1X502.5^ 

 3,908X875 

 2,049X875 

 786X784 

 Unmarked X4.054 

 Unmarked X4, 152 

 Unmarked X4, 152 



Unmarked X4i631 



10 







2 



l 



173 



X4.905 



3,908 X 875 

 1,828X1,829 

 562 X 563 

 1,074 X 563 



10 







3 

 2 





Total 



78 







In these experiments yellow an 



mals bred inter 



e have produced 



non-yellow young half of which are agouti and half of which 

 are non-agouti. It seems therefore to be wholly a matter of 

 chance whether a yellow animal heterozygous in agouti trans- 

 mits that character with yellow or apart from it. Sturtevant's 

 contrary conclusion is due in part .to his reliance on the insuffi- 

 cient numbers observed by Morgan and in part to his overlooking 

 certain of the results reported by Miss Durham. For, in addi- 

 tion to the category of matings of yellow mice cited by Sturte- 

 vant, she reports matings of sable (yellow) mice inter se which 

 produced 17 sable (yellow), 8 yellow, 5 agouti, 4 black, and 2 

 brown young, a result in harmony with that which I have de- 

 scribed. 



In the matings reported by Miss Durham in which yellow 

 parents produced only yellow young and agouti young, it seems 

 probable that one or both of the yellow parents was homozygous 

 in agouti. The same was probably true in the similar experi- 

 ments of Morgan. This would explain why all the non-yellow 

 young were agouti marked. 



As further evidence that yellow and agouti are wholly 

 independent characters may be cited experiments of my own 

 in which yellow animals evidently heterozygous in agouti were 



