DRUG ACTION UPON GENES I4I 



Possible Modes of Drug Action upon Genes 



At least three consequences may follow the action of a 

 drug upon a gene. i. The normal physiological action 

 of the gene may be reduced or abolished. 2. Mutation of 

 the gene may occur. 3. Reproduction of the gene may be 

 inhibited. If a cell changes its behaviour or nature under 

 the action of a drug it may or may not return to its initial 

 condition when the drug is removed. If the action of the 

 drug is reversible, its action is commonly said to be phys- 

 iological, whether the action is upon a gene or not. 

 If the action is irreversible it is thought to involve a mu- 

 tation, although it is usually only possible to prove this 

 when sex cells are involved. 



It is of much interest that the same or similar substances 

 may often be simultaneously i . morphogenetic evocators, 

 2. carcinogenic and 3. hormones with a physiological 

 function. For example, members of the oestrogen series 

 have all three of these activities. At present one may well 

 be inclined, on theoretical grounds, to suggest that i. and 

 2. are in fact similar processes involving the mutation of 

 genes. 



The situation is complicated by the fact that, although 

 most of the genetic phenomena with which we are accus- 

 tomed to deal are mediated by genes attached to chro- 

 mosomes and obeying the Mendelian laws, evidence is 

 steadily accumulating to show that some transmissbile 

 characteristics are carried, not necessarily by nuclear 



Cell Physiology 9* 



