Experimental Hybridizing "jy 



explanation of the assumed purity of the germ-cells in the Men- 

 delian cases, yet more careful consideration shows that in order 

 to do so certain assumptions are necessary that are not above 

 suspicion. 



It may be seriously questioned, I think, whether the germ-cells 

 of Mendehan hybrids are pure. It is true that the Mendelian 

 proportion, 1:2:1, in the second (^2) generation can be most 

 easily accounted for by assuming two kinds of male and 

 two kinds of female germ-cells, each kind existing in equal 

 numbers ; but the assumption that the two kinds must be pure 

 germ-cells meets with serious difficulties when certain results 

 are considered. It will suffice to point out here that the main 

 difficulty Hes in the behavior of the so-called extracted reces- 

 sives which ought to be a pure strain on the assumption of 

 "pure" germ-cells, but which have been shown on the con- 

 trary to contain in a latent condition the dominant character. 

 I have tried to show that the results may still be accounted 

 for even if the germ-cells of the hybrids of generation {F{) 

 are not pure in regard to any pair of contrasted characters, 

 such as gray and white, but that both characters are present 

 in all the germ-cells. The two kinds of germ-cells that the 

 hypothesis calls for may be referred to the alternating 

 dominance in the germ-cells of each of the two contrasting 

 characters. The Mendehan proportion can be accounted for 

 on this assumption as well as on the accepted interpretation 

 of pure germ-cells, and the latency of the dominant char- 

 acter in the extracted recessive can also be explained on my 

 view, but not on the other. An example may make my 

 meaning clearer. 



Suppose a white and a gray mouse are paired. The germ- 

 cells of the white mouse are white-producing, or briefly white, 

 those of the gray mouse are gray-producing, or briefly gray. The 

 fertihzed egg will contain both characters, and since the gray 

 dominates the white, the symbol G{W) will represent the con- 

 dition in the mouse itself. In its germ-cells both the gray, G, 

 and the white, W, exist, presumably combined in some way. 



