of tryptophan, we wanted also to study the reverse process, the breakdown 

 of tryptophan to indole, a reaction typical of the bacterium E. coli. For this 

 purpose we obtained, from the Bacteriology Department at Stanford, a typical 

 E. coli culture, designated K-12. Naturally, this strain was later used for the 

 mutation experiments just described so that a variety of biochemically marked 

 mutant strains of E. coli K-12 were soon available. It is also of interest that 

 Miss Esther Zimmer, who later became Esther Lederberg, assisted in the 

 production and isolation of these mutant strains. 



Another interesting coincidence is that F. J. Ryan spent some time on 

 leave from Columbia University at Stanford, working with Neurospora. Shortly 

 after I moved to Yale University in 1945, Ryan encouraged Lederberg, 

 then a medical student at Columbia who had worked some with Ryan on 

 Neurospora, to spend some time with me at Yale University. As all of you 

 know, Lederberg^ was successful in showing genetic recombination between 

 mutant strains of E. coli K-12 (13) and never returned to medical school, 

 but continued his brilliant work on bacterial recombination at Wisconsin. 

 In any case, the first demonstration of a process analogous to a sexual process 

 in bacteria was successful only because of the clear-cut nature of the genetic 

 markers available which permitted detection of this very rare event, and 

 because of the combination of circumstances which had provided those selec- 

 tive markers in one of the rare strains of E. coli capable of recombination. In 

 summing up this portion of this case history, then, I wish only to emphasize 

 again the role of coincidence and chance played in the sequence of develop- 

 ments, but yet more strongly to acknowledge the even greater contributions 

 of my close friends and associates. Professor Beadle and Professor Lederberg, 

 with whom it is a rare privilege and honor to share this award. 



Now for a brief and necessarily somewhat superficial mention of some of the 

 problems and areas of biology to which these relatively simple experiments 

 with Nerospora have led and contributed. First, however, let us review the 

 basic concepts involved in this work. Essentially these are (i) that all bio- 

 chemical processes in all organisms are under genie control, {2) that these 

 overall biochemical processes are resolvable into a series of individual stepwise 

 reactions, (3) that each single reaction is controlled in a primary fashion by a 

 single gene, or in other terms, in every case a i : i correspondence of gene and 

 biochemical reaction exists, such that (4) mutation of a single gene results 

 only in an alteration in the ability of the cell to carry out a single primary 

 chemical reaction. As has repeatedly been stated, the underlying hypothesis, 

 which in a number of cases has been supported by direct experimental evidence, 



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