Genie and Non-genic Parts of the Chromosome 49 



Since, in all these cases, specific extracted DNA is the trans- 

 forming agent, the supreme importance for the problem of the genie 

 nature of DNA is obvious. Ephrussi-Taylor rather understates it as 

 follows: "We have here the beginnings of a very unique system of 

 genetical analysis. It is a system in which, as yet, no bridge can be 

 seen leading over into classical genetics, but which is promising 

 enough to be an end in itself." The simple and consistent facts re- 

 ported thus far are not the only ones known. Ephrussi-Taylor has 

 worked with cases in which the transformation produces a third type, 

 diflFerent from both the treated and the treating types. An explanation 

 of the entire phenomenon must take such facts into account. 



Lederberg (1952; Cavalli and Lederberg, 1953; Lederberg and 

 Tatum, 1953) has introduced the term "transduction" to include 

 bacterial transformation of the pneumococcus type as well as a 

 remarkable new type. Zinder and Lederberg (1952) described how 

 the transfer of antigenic properties in the bacterium Salmonella 

 typhimurium from bacterium to bacterium can be eflFected by a non- 

 killing bacteriophage. The phage must pull out some genetic particle 

 from its host and deposit it in another host as a genie property. 

 Lederberg thinks that the process — also the one in pneumococcus — 

 amounts to a hybridization which involves not whole cells (i.e., their 

 germ plasm) but only parts of the genie system (therefore only a 

 single character can be transduced in one experiment). 



These amazing facts raise the question whether bacterial genetics 

 is not based upon an at least partly different principle. If a virus-like 

 body is used to transfer bodily what might be called, a single locus, 

 we could speak of a kind of fertilization-ersatz with features com- 

 pletely different from those in the standard type of zygote formation. 

 If this is true, bacterial transformation might be a part of this 

 completely different genetic system or, in the terminology of Leder- 

 berg, transformation and transduction would be essentially the same 

 thing. This conclusion, at which we hinted above, has been empha- 

 sized by Zinder (1953). The greatest similarity is in the effect: namely, 

 a stable new character brought about by the incorporation of its 

 causative agent into the genome by a process involving the replace- 

 ment of the homologous material. But the agents which bring this 

 about are dissimilar: specific DNA-tes in transformation, and a virus 

 or phage of unknown properties in the transduction. It seems that 

 in both cases any bacterial character can be transferred, though usu- 

 ally only singly; and it seems certain also that they replace already 



