524 JOSHUA LEDERBERG 



application of genetic techniques to the elucidation of unusual life-cycles in 

 diverse bacteria (Braun and Elrod, 1946, Dienes, 1946) cannot fail, how- 

 ever, to be most fruitful. 



The evolutionary significance of gene recombination has been made so widely 

 familiar by Dobzhansky's book (1941), and adequately discussed, more re- 

 cently, by Muller (1947), that it would be impertinent to do more than 

 simply refer to these papers. 



SUMMARY 



The recombination of genetic factors and their segregation into prototroph 

 recombinants of Escherichia coli have been studied. It was found that genetic 

 markers behaved as if they were part of a system of linked genes. Some evi- 

 dence for linear order of genes was obtained. Each of 15 factors studied fell into 

 the same linkage group. Data are given in detail for the segregation of factors 

 involved in the biosyntheses of biotin, methionine, threonine, leucine, or thi- 

 amin; in the fermentation of lactose, and in resistance to bacterial viruses Ti 

 and T6. On the basis of these data a tentative 8-point genetic map of the chro- 

 mosome of E. coli is presented. 



acknowledgements 



The author is deeply indebted to many of his colleagues and friends, too 

 numerous to mention, for stimulating discussions of the problems discussed in 

 this paper. They are numbered, by and large, among the participants and 

 discussants of the 1946 Cold Spring Harbor Symposium on Quantitative 

 Biology. He is indebted to Dr. Maclyn McCarty for a generous sample of 

 purified desoxyribonuclease, and to Drs. S. E. Luria and M. Demerec for 

 cultures of the bacteriophages used in this investigation. He owes much of the 

 genetic analysis to the criticism of Dr. K. Mather of the John Innes Horti- 

 cultural Institution. Above all, he is indebted to Professor E. L. Tatum 

 for the opportunity and much of the stimulus to do these experiments. 



literature cited 



Anderson, E. H., 1946 Growth requirements of virus-resistance mutants of Escherichia coli 



strain "B." Proc. Nat. Acad. Sci. 32: 120-128. 

 Avery, 0. T., C. M. MacLeod, and M. McCarty, 1944 Studies on the chemical nature of the 



substance inducing transformation of pneumococcal types. J. Exp. Med. 79: 137-158. 

 Boivin, A., and R. Vendreley, 1946 Role de l'acide desoxy-ribonucleique hautement poly- 



m^ris^ dans le determinisme des caracteres hereditaires des bacteries. Signification pour la 



biochemie g6n£rale de l'he>6dit6. Helv. Chim. Acta 29: 1338-1344. 

 Braun, A. C., and R. P. Elrod, 1946 Stages in the life history of Phytomonas tumefaciens. J. 



Bact. 52: 695-702. 

 Demerec, M., and U. Fano, 1945 Bacteriophage-resistant mutants in Escherichia coli. Genetics 



30: 1 19-136. 

 Dienes, L., 1946 Complex reproductive processes in bacteria. Cold Spring Harbor, Symposia on 



Quantitative Biology 11: 51-59. 

 Dobzhansky, Th., 1941 Genetics and the Origin of Species. Rev. Ed. xviii-l-446 pp. New York: 



Columbia Univ. Press. 

 Gray, C. H., and E. L. Tatum, 1944 X-ray induced growth factor deficiencies in bacteria. Proc. 



Nat. Acad. Sci. 30: 404-410. 



162 



