Morgan, Are the Germ-Cells of Mendelian Hybrid« "Pure"? 295 



attempt to account in an otherway i'or the results, and in so far as 1 tiiotl 

 fco show fchat pure gametes were not to be expected from extrac- 

 ted dominant forms, I believe I may have found the clue that will 

 lead to a möre probable Solution of the problem. 



Cuenot has shown in the following way that yellow dominates all 

 other eolors. Assnming, as he does, that all yellows are dominant 

 recessives, YB for instance, he finds when these are crossed with a pure 

 strain, gray let us say, that he gets 50 per. cent. yellow and 50 per. 

 cent. of the other color, (or eolors when more than one is present). 

 Cuenot 's equation for this would be 



CY CG 



CG CG 



CYGG CGCG 



Since CYCG gives yellow, the yellow is thus shown fco domi- 

 nate the gray gamete. I should express the same result in a 

 somewhat different way thus: 



Y(G) (Y)G 



G G 



Y(G),G (Y)G,G 



The result is the same, so far as the formulae show the domi- 

 nance of the yellow over gray. If, as I suppose, extraeted yellow 

 dominants are also formed, we should expect them, from analogy 

 with other eolors, to produce when inbred only yellow mice, and 

 also when crossed with mice of other eolors; but as this was 

 found by Cuenot not to be the case, he assumes, as has been 

 said, that dominant yellow mice are not produced. There is, ho- 

 wever, another way in which we may account for the results. li 

 we assume that extraeted dominants are formed in the. case of 

 yellow mice, as in all other cases, but that the two eolors do not 

 remain in the usual relation of dominance and latency, but alter- 

 nately become dominant and latent in the germ-cells, we can 

 account for all of Cuenot 's facts. Thus an extraeted yellow domi- 

 nant Y(G) produces germ-cells Y(G) and (Y)G, which will give on 

 inbreeding, if in equal numbers, three yellows to one gray 1 ). 

 When these yellows are crossed with other eolors the expeetation 

 would be 50 per. cent. of each. The results are those that 

 Cuenot's yellow mice give. My assumption, in regard to the 

 behaviour of the germ-cells^ of the yellow mice, is not purely ar- 

 biträr}', for there are cases on record of other eolors in which 



1) If as many Y(G) are produced as (Y)G. If not, more of the offspring will 

 be gray. Cuenot insists that there is a defieiency in yellow mice, when yellows 

 are inbred. May not this disparity be due to the smaller number of the yellow 

 gametes formed by the yellow mice? Possibly the extraeted dominants and the 

 dominant recessives might be separated by taking into consideration the relative 

 number of yellow and gray (or black) offspriDg that they produce. 



