8 



On the Inter-relations of Genetic Factors. 



that there must be an " order of precedence " among the factors composing 

 such a system, and the suggestion is plausible that this order will follow 

 the grade of coupling in which the factors are accustomed to be linked. 



It will be observed that, given a system under which a pair of factors 

 are coupled, it is possible to produce the system under which the same pair 

 repel each other. For all that is necessary is to breed together the rarer 

 terms of the coupled series, viz., Ab and aB. 



From the repelling system, on the contrary, in the absence of a fresh 

 variation, we have no obvious way of constructing the coupled system. This 

 consideration has an obvious application to those cases in which sex operates 

 as a repelling factor. In the fowl, the canary, and Abraxas grossulariata, 

 femaleness thus acts as a repelling factor against various elements 

 determining pigmentation ; and our experience of the plants leads us to 

 suppose that if the factors involved could be built up in the right 

 combinations, femaleness might be coupled with the factors it now repels. 



Extraordinary consequences, both to the distribution of the sexes, to the 

 distribution of factors between them, and perhaps to the causation of fertility, 

 must be anticipated if this condition could be fulfilled. There may be an 

 indirect way of actually accomplishing these results. For, seeing that sex 

 in the fowl acts as a repeller of at least three other factors, when birds are 

 built ,up so as to be heterozygous for several of these, some of them may be 

 found able to take precedence of the others in such a way as to annul the 

 present repulsions, with subsequent coupling as a consequence. 



