164 RADIATION GENETICS 



Dr. Grahn: The United Nations, in conjunction with the World Health Organiza- 

 tion, is interested in the problem of effects of low-level radiation in man. 1411 The 

 United National Scientific Committee on the Effects of Atomic Radiation is also 

 interested in improving the collection of vital statistical data so that it will be of some 

 value in human or genetic studies. I know of no specific program or plan to bring 

 together the diverse efforts of different countries other than those agreed upon in an 

 informal way, such as might be arranged between the United States and the United 

 Kingdom and Canada. 



Dr. Gowen: In discussing rates of mutation, you placed quite heavy emphasis on 

 the seven loci in mice. Knowing what has been learned about mutations in Drosophila 

 and realizing the variations possible when one considers that crossing over occurs 

 within the gene, so to speak, would you put a premium on the seven loci, or would you 

 prefer to have a much more general survey of the mutation frequencies for as many loci 

 as one can keep under reasonable control ? 



Dr. Grahn: What do you mean when you speak of premium, Dr. Gowen? 



Dr. Gowen: Premium in the sense that it would be strange indeed if such a group 

 of loci were representative or even suggested the range of mutation rates or the types of 

 changes which may be expected to occur in, say, mammals or man. 



Dr. Grahn : Certainly data on more loci are desirable if for no other reason than 

 to give assurance that these seven loci and the mean or median rates of mutation 

 derived therefrom are reasonable descriptions of the average mutation rate for the total 

 genome. This is neither cheap nor easy, so the solution of the problem is not obvious. 

 Total gametic methods are not too efficient either. In other tester stocks that have 

 been or can be synthesized, their reduced viability, reduced fertility, over-lapping 

 phenotypes, etc., make the problem additionally very difficult to solve. 



Dr. Yerganian: Dr. Grahn's remarks on reverse-lighting patterns of illumination 

 in animal-breeding rooms should be supported wholeheartedly for the benefit of the 

 investigator who wishes to initiate convenient and controlled matings. 1462 



Dr. Lederberg : It seems to me there has been such a frenzy of interest in radiation- 

 induced mutation that we are very seriously neglecting the other environmental factors 

 which, from a practical point of view, may be much more important to man. I am 

 talking about chemically induced mutation and antimutation effects. As far as I can 

 tell, there has been a studious neglect of the very well-documented observations that 

 mutation rates in bacteria, and very much more recently in Drosophila, can be markedly 

 influenced by the presence of various purines in the diet. Furthermore, the compound 

 adenosine will go so far as to reduce the mutation rate in bacteria by the factor of a 

 half. Now if you are concerned about the incidence of mutation in the human popula- 

 tion, I think it is reasonably plain that you could exert on a global basis a much more 

 significant effect by alteration of diets which would have some effect on the spontaneous 

 mutation rate than we are now likely to accomplish by small changes in the environ- 

 mental radiation hazard. I am not saying we are not justified in making strenuous 

 efforts to reduce the radiation hazards to manageable levels; but I feel now that there 



