Lederberg • Genetic Transduction 



rare. Partly for this reason, and partly 

 because the experimental organisms 

 have usually been economicalh- unim- 

 portant, recombinational techniques 

 have had more analytic than practical 

 utility. (Artificial serotypes in Salmo- 

 nella have been of some use in the 

 preparation of diagnostic scrums.) The 

 vast applications of genetics in practical 

 agriculture are, however, a sufficient 

 portent of what may be accomplished 

 in due course with the microbes that 

 are important in medicine and indus- 

 try. 



Some of the hopes that have been 

 expressed, however, are too extravagant 

 in the light of present knowledge, for 

 example for the massive transformation 

 of virulent or drug-resistant bacteria in 

 an infected host to more innocuous 

 forms. To be therapeutically effective, 

 such transformations would have to 

 involve virtually every bacterium, 

 which is too much to ask of a recombi- 

 nation process (barring the excep- 

 tional examples of lysogenic conver- 

 sions). A similar misconception has 

 provoked the suggestion that transduc- 

 tion could account for the spread of 

 drug-resistance from one mutant cell 

 to a large population (a result that 

 needs no elaborate explanation other 

 than selection). In every case so far, 

 genetic transduction is achieved at the 

 expense of the life of the donor cell: in 

 the most favorable cases, the DNA or 

 the lambda from one or a few bacteria 

 has been enough to transform a single 

 recipient, which speaks for the recovery 

 of much of the original genetic ma- 

 terial. 



So far, no definite case of trans- 

 duction has been reported for higher 

 organisms. Claims that DNA from 

 tumor cells would induce tumors in 

 normal mouse tissues are controversial 

 but they do illustrate the impact of 

 transduction on experimental cancer 

 research. The concept may also have 

 some bearing on mysterious changes in 



263 



tumor cells that are transplanted to 

 new hosts. And speculations correlating 

 the pneumococcus transformation to 

 cmbr\onic inductions perhaps have to 

 be inverted and reviewed ^^'ith the ge- 

 netic understanding of the former. 

 How^ever, before a convincing search 

 for transduction in higher organisms 

 can be executed, efficient selective 

 methods will have to be developed as 

 they have been for bacteria. 



The question of whether transduc- 

 tion is unique to the bacteria, or occurs 

 more generally, is important for its 

 bearing on general genetic theor^^ It 

 has been suggested that the postulated 

 "chromosomes" of bacteria and viruses 

 are chemically and structurally less 

 elaborate than the cvtogenetically veri- 

 fied chromosomes of higher plants and 

 animals. However, the generalization 

 of concepts and techniques learned 

 from these organisms has been the 

 most productive approach to the analy- 

 sis of transduction in bacteria. Con- 

 versely, transduction has pointed up 

 the weaknesses of some traditional 

 formulations of chromosome behavior. 

 In crossing-over, for example, can we 

 believe that two chromosomes will 

 regularly break at precisely correspond- 

 ing points? The impending translation 

 of genetic differences as chemical (or 

 grosser structural) differences in DNA 

 has also provoked a re-examination of 

 the concept of the "single gene." We 

 are reminded again of the first prin- 

 ciple of genetics, that we cannot recog- 

 nize genes directly but only their differ- 

 ences. In turn, we should not insist on 

 genes as self-reproducing units, but as 

 units or markers of a more complex 

 self-reproducing system. Nevertheless, 

 the representation of genie differences 

 in chemically purifiable DNA is the 

 closest approach to the reduction of 

 genetics to biochemistry, an enterprise 

 which can challenge the skills and 

 imaginations of specialists in a dozen 

 sciences. 



