CROSSING. 



65 



character in Primula sinensis, which could be thought to be 

 due to progressive mutation. This is the absence of the yellow 

 eye as seen in "Queen Alexandra" Gregory found that the 

 hybrids between such plants and normals, when self-fertilized, 

 gave a mono-hybrid 3 : 1 ratio. In his books on "Problems 

 of genetics" Bateson discusses this point. On page 92 he writes: 

 "There is no real doubt that it came into existence by the 

 definite addition of a new factor, for if it was simply a case 

 of the appearence of 

 anew character made 

 by combination of 

 two previously exist- 

 ing complimentary 

 factors we should ex- 

 pect that, when Queen 

 Alexandra was sel- 

 fertilized a 9 : 7 ratio 

 would be a fairly 

 common result, which 

 is not in practice 

 found". 



Now here we must 

 again distinguish be- 

 tween the original 

 hybrid, and later in- 

 dividuals with the 

 same character. For 

 if the dominant char- 

 acter in question 

 really results from 

 a development to 

 which two genes contribute, which are not found together 

 in the genotype of other species, hybrids with Queen Alex- 

 andra as one parent, and exhibiting the new character, 

 would not in self-fertilization produce a 9:7 ratio, but a 

 3 : 1 one, only one gene being concerned. Only those plants 



Fig. 9. 

 Diagram illustrating the origin of a "dou- 

 ble recessive" noveltv, and the fact that it 

 closely simulates mutation, and cannot 

 readily be distinguished from it even by 

 test matings. 



