58 MUTATIONS 



Atwood: I would say that even per cell division, the rates may well 

 be comparable. One could find many examples of comparable rates if 

 one looks for them. 



Freese: I think you should stick to your cautious statement. The 

 frequency of the elementaiy mutagenic processes may very well be 

 different in different organisms. Responsible for this difference may be 

 different base analogs or other chemicals. We have no reason to assume 

 that the mutation rates should be alike. 



Demerec: As you probably know, strains LT2 and LT7 of Salmonella 

 differ considerably in their rates of spontaneous mutability. The reason 

 for this difference is genetic, namely, the presence of at least one 

 mutator factor and probably more than one in the LT7 strain. One 

 of these factors has been identified as a gene located near threonine 

 on the genetic map (22). Dr. C. Kirchner has observed that the 

 supernatant of the strain carrying the mutator gene is mutagenic. He 

 is working on extraction and analysis of the mutagenic substance. It 

 appears to be a purine analogue. 



Novick: One thing that disturbs me in this kind of discussion is 

 that we look at a man with a much higher degree of care than we do a 

 bacterium. If we looked at the bacterium with the same kind of care 

 we look at a human, we probably would find all kinds of "mutations" 

 occurring at 10"^ or thereabouts. 



Goodgal: Yes, from the number of different suggestions which have 

 been given, I just wonder if we can say anything with regard to the 

 magnitude of the variables. 



Zamenhof: The term, "mutation rate per generation," which should 

 be universal if one wants to apply it also for evaluating the strength 

 of mutagenic agents, cannot be applied when one deals with dis- 

 continuous events (43). Perhaps the mutation frequency, with the 

 description of conditions, would be more universal as a term. But 

 neither "the generation" nor "the time" is more important than any 

 other of these conditions in many mutagenic processes. For the same 

 mutagenic agent, you can have conditions where the term "per genera- 

 tion" is meaningful and other conditions where it is meaningless. 



Auerbach: I just wanted to say that I agree, but it is only a termino- 

 logical point. I always feel rather strongly about the word "mutation 

 rate." When you have treated with X-rays or instantaneous or short ex- 

 posure to mustard gas, this is meaningless. One should call it mutation 

 frequency. 



Atwood: Per dose? 



Zamenhof: What I meant was this: there are mutational processes 



