94 ANNALS NEW YORK ACADEMY OF SCIENCES 



find no records in my notes that show this to be the case. The color has 

 appeared sporadically and does not appear to come through the yellows 

 of the yellow crosses that have yielded relatively few mice compared with 

 other combinations. Moreover, if the result had been due to yellow, we 

 would expect it to appear only in the mice directly derived from yellow 

 crosses, but this is not apparent. 



Crossing Extracted Gray and Black to Test the Hypothesis of 

 Alternate Dominance and Eecession 



In order to account for the two kinds of germ cells produced for each 

 pair of characters by Mendelian hybrids, I suggested in 1905 that if 

 instead of treating the question of segregation as the result of the sepa- 

 ration of material factors, we treat the process as due to alternate domi- 

 nance and recession of the paired characters in the gametes, we arrive at 

 the same end results, viz., the formation of three classes of individuals in 

 the second generation. This was an attempt to give a dynamic conception 

 of the process of segregation instead of the conventional idea of separation 

 of material particles as the basis of Mendelian inheritance. I advanced 

 this view primarily to escape Cuenot's hypothesis for the inheritance of 

 yellow which called in the aid of selective fertilization. Cuenot assumed 

 that a yellow-bearing sperm never fertilized an egg bearing this same 

 factor for yellow, hence all yellow mice arise through the union of two 

 germ-cells only one of which carries the factor for yellow. Selective fer- 

 tilization seemed to me highly improbable in itself, and if true in general 

 for other characters it would lead to all sorts of irregularities in Men- 

 delian inheritance. It now appears that the particular ratio of three to 

 one, given by Cuenot 2 as the probable ratio for yellow in the second 

 generation, is in reality a ratio of two to one, as Castle and Little have 

 recently pointed out, so that the grounds for the original assumption by 

 Cuenot fall to the ground. I pointed out at the same time certain logical 

 consequences that followed, if my argument for alternate dominance and 

 recession were valid, and I set to work to put the hypothesis to the test 

 of fact. 



The example that I used in my paper to illustrate the hypothesis of 

 alternate dominance and recession, namely, the inheritance of albinism 

 versus pigmented coat, was unfortunate, since it is generally conceded now 

 that albinism is not due to the absence of the color determiner (gray or 

 black, etc.), but to the absence of another factor, the color producer. It 



* Cuenot discussed also the possibility of the two to one ratio. 



