LINKAGE OI- I'OLVGENHS 



since 9 exceeds half of 15-7, we have no reason to doubt that the 

 heritable difference between S and O is wholly due to differences 



in nuclear genes 



What position have we now reached? First, we see that con- 

 tinuous variation is capable of being caused by nuclear genes, which, 

 to be sure, work in special systems. Furthermore, we see that the 

 heritable part of this variation is wholly due to such genes. We see 

 this both from the lack of differences between reciprocal crosses and 

 from the balance-sheet of variation which the linkage experiments 

 enable us to draw up. Finally, we have been able to infer the action 

 of individual genes although these genes are not individually recog- 

 nizable. We been able to do so simply because these individual 

 genes are all transmitted in the same way, by the very mendelian 

 inheritance whose principles they were at one time supposed to 

 contradict. 



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 GALTON, F. 1889. Natural Inheritance. London. 

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77 



