An Introduction to a Biology 



call M, which determines that the organism which develops 

 from the germ-cell shall be a mouse, and another A, which 

 makes that mouse an albino. And similarly in the case 

 of the waltzer, its germ-cell contains an M similar to that 

 of the albino, and a factor W, which makes it what it is, 

 a waltzer with pink eyes and fawn-and-white coat. Now 

 M and M are supposed to be the same ; but A and W different 

 and antoganistic. So that when an albino and a waltzer 

 are mated it is a question which of the two factors which 

 are antagonistic, W oi A, will be manifested in the offspring. 

 What happens, according to Von Guaita's theory, is that 

 the two factors W and A struggle, and neutralise each other 

 so that neither of them is manifested in the offspring, leaving 

 the two iUf's, which are similar and compatible, in sole pos- 

 session of the field. This theory accounts in a very ingenious 

 way for the character of the hybrid ; and doubtless some 

 elaboration of it could be suggested which would account 

 for the reproduction of the three categories 00, OC, and 

 CC in the next generation. 



The theory put forward by Bateson two years ago to ac- 

 count for these phenomena is that there is in the germ-cell of 

 an albino a factor determining albinism, which he calls g, and 

 similarly that there is a factor g' in the waltzer, determining 

 its colour characters, which we have already called 00, 



The result of the union of g and g' is a hybrid g' g, whose 

 character we have already denoted by CC. The result of 

 the union of g' and g — the production of a form more different 

 from either of them than they are from each other — is said 

 to be a specific result in the sense that the production of 

 water is said to be the specific result of the union of Hg and 0. 

 But the most striking part of this theory is that which refers 

 to the germ-cells of the hybrid. According to it, 50 % of 

 the germ-cells of the hybrid bear the factor g' and 50 % g. 

 Now the result of the union of two hybrids each containing 

 50 % gr' + 50 % g germ-cells is the production of offspring 

 falHng into the following categories in the proportions in- 



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