GENES AND DEVELOPMENT I57 



to the whole organism. They are singled out from other genes, not 

 because they are necessarily fundamentally different but because they 

 are particularly interesting, just as vitamins and hormones are singled 

 out from the group of food substances and chemical constituents of the 

 plasma. 



We shall see that every gene probably affects several different pro- 

 cesses, and in discussing the action of a gene we shall usually be con- 

 centrating on one only of the whole set of reactions in which it is 

 concerned. We should therefore, to be strictly accurate, speak not of 

 substance and pattern genes but of substance and 'pattern aspects of 

 genie action, but the gain in accuracy is not worth the clumsiness 

 which such locutions would introduce. The context will make clear 

 which aspect of the gene's total activity is being referred to. 



