g6 Experimental Zoology 



AY AY, and CYAY. In other words, selective fertilization 

 occurs. 



It seems to me that this is improbable and that a simpler 

 assumption may account for the results. Cuenot's yellow mice 

 were obtained through an albino of unknown ancestry. He 

 crossed them with gray (or with black) mice, and obtained 

 dominant yellow mice, to which he assigns the formula CYCG. 

 These when inbred should give, according to Cuenot, on the 

 theory of disjunction of the gametes, CY- and CG-gametes. 

 The offspring would then give the Mendehan proportion — 



I CYCY+2 CYCG^i CGCG. 



But no mice represented by CYCY were obtained. It seems 

 to me more probable from the results that the yellow does not 

 separate from the other colors, and if so all the germ-cells 

 would be on my view CY(CG) or (CY)CG. Such forms 

 inbred would not give CYCY, as Cuenot assumes, but the 

 dominant heterozygote CY(CG). 



This point of view assumes that the yellow is so slightly 

 prepotent in the extracted dominant, CY(CG), that the gray 

 may dominate in half the germ-cells, giving CY(CG) and 

 CG(CY). If this is true, gray mice would appear in one- fourth 

 of the offspring of these dominants. The yellows differ on 

 this point of view from all other extracted dominants in the 

 failure of the yellow to remain dominant in the germ-cells. 



Schuster has made a number of pairings between gray and 

 white mice. Seventy of such families (F^) were gray ; ^ two 

 families contained yellow mice and gray mice; one family con- 

 tained four chinchilla mice only ; and one contained two chin- 

 chillas and one gray. The appearance of these yellows in the 

 first hybrids is ascribed by the author to the presence of yellow 

 in the white parents, — the yellow dominating the gray of the 

 first hybrids. Whether the same explanation will account for the 

 chinchillas is not known, because the dominance of the chin- 

 chilla has not been tested. 



^ Containing 342 mice. 



