SFX IN BACTERIA— GENETIC STUDIES 17 



such as have been observed and speculated about in many bacteria. 

 The possibility of a mating process involving a rapid conjugation and 

 separation of the parent cells, without the intervention of special 

 gamete or zygote structures, has not been excluded and is perhaps 

 most likely. 



The recently reported work of Hayes may throw further light 

 on the conjugation process. Working with a single pair of K-12 

 stocks, Hayes (1952a) found that streptomycin treatment sterilized 

 one (58-161) without affecting its recombination potency, but com- 

 pletely abolished recombination potency of the other (W677), and 

 he postulated a unidirectional transfer of metabolically inert genie 

 material from 58-161 to W677. The results of later studies (Hayes, 

 1952b) using ultra-violet irradiation for cell inactivation and stimula- 

 tion of recombination (Clark et al., 1950) were consistent with this 

 hypothesis. He has suggested that the recombination may involve only 

 a limited transfer of genie material, through a process which may 

 not require the participation of two intact cells. 



Granted the ability of E. coli K-12 to undergo a sexual recom- 

 bination of genetic characters analogous to that found in other 

 organisms, even if the morphological basis is still obscure, can the 

 analogy be carried further? What evidence exists bearing on a chro- 

 mosomal organization of the genes in E. coli} In all organisms that 

 have been adequately studied, the genes are arranged in a linear 

 order on chromosomes, whose distribution at cell division and during 

 the formation of gametes follows very precise laws. It is difficult, in 

 fact, to conceive of any other arrangement of the genes that would 

 permit their regular and orderly distribution to the products of each 

 cell division, without an uneconomical redundancy of the genetic 

 factors for different traits. But aside from these speculations, there 

 is considerable experimental evidence that the genes of E. coli are 

 organized in linear order on one or more chromosomes (Lederberg, 

 1947; Rothfels, 1952; Lederberg et al, 1951). 



In the crosses mentioned so far, all the differences between the 

 parents are directly involved in the selection of recombinants, so that 

 we had no opportunity to investigate the segregation of factors whose 

 expression is not enforced by the selective method. A number of 

 mutant characters have been discovered, however, which are indif- 

 ferent to plating on minimal medium. They include differences in 

 the fermentation of various sugars, resistance to antibiotics, and resist- 



