Discussion of Session V 



HERBERT H. KRAMER 



Purdue University, Lafayette, Indiana 



IN a short time Doctor Stephens will attempt to summarize the 

 proceedings of the past few days. In the meantime, however, some 

 speculation on how our knowledge of a gene today might be trans- 

 lated into what we do with it in the future would seem to be in 

 order. 



This symposium has emphasized the concept of gene complex- 

 ity. This concept has long been widely held and in itself represents 

 little advance. The remarkable advance in recent years has been in 

 the elucidation of the nature of the complexity. The nature of the 

 gene has been attacked on almost every conceivable level, molecular, 

 chromosomal, nuclear, cellular, organism, and population. In each 

 case the weapon has been the mutant allele, which for our purpose 

 may be defined as a deviant from an undefined normal form. 



Through classical studies of recombination, the one genetic 

 phenomenon unique to, and equally important to, all levels of gene- 

 tic and plant breeding research, the gene, as a unit of function has 

 been raised to a level of structural sophistication which seems ade- 

 quate to provide the code for the complex compounds through 

 which it must mediate its effect. 



At the cistron level, hope for controlling the direction of change 

 resides in the degree of specificity of reaction to different muta- 

 gens. The evidence for such specificity has been thoroughly reviewed 

 by Doctor Smith. Paradoxically, the very studies in bacteriophage 

 which demonstrate so convincingly the extreme specificity of intra- 

 locus reactive sites would argue that similar reactive sites within 

 any cistron would be reactive and lead to inter-locus nonspecificity 

 unless some effect of molecular organization on reactive sites is 

 assumed. This focuses attention on one of the most serious gaps in our 

 knowledge, that of relating the intra-locus or site specificity demon- 

 strated in microorganisms to the spectra of inter-locus mutants 

 observed for different mutagens. Whatever the final explanation, 

 it is certain that induced mutations will play the major role in 

 resolving the problem. It is likely that we will continue to look to 



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