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Comments 



Auerbach: I should like to throw in a word of caution about the so- 

 called "true specificity" of Doctor Smith. I think one has to distinguish 

 between the result, the mutation, and the process by which it is 

 obtained. If one accepts the DNA model of the gene and the base-change 

 model of mutation, then the result — a change of one allele into another — 

 certainly is specific; but this does not mean that the action of the chem- 

 ical on the DNA is specific. In fact, there is so far no proof that this 

 is so in any case, although there is strong presumptive evidence for it 

 in the case of bacteriophage. In other cases, reported for bacteria and 

 fungi, mutagen specificity might reside at any one of the steps by which 

 the primary chemical event is transformed into a detectable mutant. 

 Doctor Haas has dealt with some of these steps, and there may be more 

 of them. In some cases it could, in fact, be shown that the detected 

 mutagen specificity depended on residual genotype, plating medium, 

 or different kinds of pretreatment. This skeptical attitude to the theo- 

 retical interpretations of mutagen specificity does not imply a corre- 

 sponding skeptical attitude to the possibility of obtaining specific types 

 of desirable mutants by chemical treatments. I think, however, that the 

 best hope for success in this field lies in attempts to find specificity at 

 some of the later steps in mutagenesis. I should recommend strongly to 

 investigate the influence of treated stage and experimental conditions 

 on the mutation spectrum produced by a given chemical mutagen. 



