LATENT CHARACTERS 195 



proves to be well established, is likely to be of great 

 theoretical interest. 



When CJ . CG (or CJ . CN) is crossed with CJ 

 (or CN), since yellow is dominant, equal numbers of 

 yellow and of grey (or black) offspring are to be ex- 

 pected, and in various crosses of this nature Cuenot 

 actually obtained 177 yellows and 178 blacks or greys. 

 Hence we may deduce that the heterozygote yellow 

 was giving off the expected proportion of gametes 

 bearing the yellow character (i.e., 50 per cent.). 



When such heterozygous yellows are bred together 

 the expected result would be as follows : 



CJ . CG x CJ . CG = C/.C/ + 2 CJ . CG + CG . CG 

 3 yellow i grey 



Eighty-one yellow mice were actually obtained in 

 this way. Among them some twenty-seven would 

 naturally be expected to be pure dominant, and to give 

 yellow only when crossed with black or grey indi- 

 viduals. To Cuenot's astonishment, he found on making 

 the necessary crosses that every one of these eighty- 

 one yellows gave some black or grey among its off- 

 spring; not one of them was a pure homozygous 

 yellow. 



The only way in which this result can be explained 

 at present is by supposing that there is some obstacle 

 to the fertilization of one yellow-bearing gamete by 

 another gamete of the same kind. The combinations 

 CJ x CG and CG x CG take place, it would seem, 

 readily enough, but there is some mutual repulsion 

 between CJ and CJ which prevents their union. We 



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