GENETIC ASPECTS OF DRUG RESISTANCE 



M. Demerec 



Carnegie Institution of Washington, Department of Genetics, 

 Cold Spring Harbor, New York 



If the problem of origin of bacterial resistance to drugs had 

 arisen recently, instead of about ten years ago, it would have 

 been a relatively simple matter to plan appropriate experi- 

 ments to elucidate the role played by genetic mechanisms in 

 the development of such resistance. A decade ago, however, 

 genetical research with bacteria was in a very early stage, and 

 it was still an open question whether or not the hereditary 

 mechanism operating in bacteria would prove to be the same 

 as the mechanism that had been demonstrated in higher 

 organisms, including fungi. Since then, ample evidence has 

 been accumulated to justify the conclusion that the genetic 

 mechanism in bacteria is similar to that in higher organisms. 

 This conclusion is further strengthened by the results of 

 studies made with bacterial viruses, which can be crossed 

 more easily than bacteria. In such crosses, using easily dis- 

 tinguishable markers, one may identify classes of offspring 

 representing the two recombinant types as well as the two 

 parental types (Hershey, 1946; Hershey and Chase, 1951). 

 Further anatysis has shown that the proportions in which the 

 four classes are represented agree with expectation based on 

 Mendelian segregation (Visconti and Delbriick, 1953). More- 

 over, the results of experiments using several markers (Hershey 

 and Rotman, 1948) reveal the existence of linkage relation- 

 ships. Taken together, these findings indicate that the basic 

 genetic process in bacterial viruses — the lowest living organ- 

 isms known — is similar to that with which we were already 

 familiar in all higher organisms. Thus it is reasonable to 

 suppose that the basic genetic mechanism is the same in all 

 living organisms, not excluding bacteria. This basic genetic 



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