322 GENE MUTATIONS CAUSED BY RADIATION 



radiation in producing gene mutations in mammals, Paula Hertwig's 

 work clearly shows the existence of the effect in mice, and her data indi- 

 cate it to be not so very different in magnitude from that in Drosophila. 

 That is, one gets the impression that the per genome frequency of gene 

 mutations induced by a given dose may be somewhat smaller than in 

 Drosophila, but probably not by as much as one order of magnitude. It 

 will be most important, and most difficult, to obtain a more exact esti- 

 mate in such an organism. We believe, however, that the investigations 

 of Russell and his group, described in a parallel paper in this symposium, 

 will in time supply the first really key data of the kind needed.* 



Despite the urgent need for more exact data, however, enough is al- 

 ready known about mutation frequencies to allow the conclusion to be 

 drawn that, if these frequencies per generation, both in untreated ma- 

 terial and in that exposed to a given dose of radiation, were similar in 

 man and Drosophila, the ultimate effect on human populations of those 

 doses to which they are likely (if present trends continue) to become 

 exposed, would in its totality be very serious. In fact, the same con- 

 clusion appears to follow, although with a much greater margin of error, 

 even on the basis of the very meager w^ork with mice already reported. 

 For an understanding of this, it is necessary to consider the manner in 

 which mutations express themselves and undergo elimination, and the 

 character of the consequent effect on the population in general. In this 

 way light will at the same time be thrown on the nature of the mistakes 

 which have been made by prominent non-geneticists, in attempting to 

 give the lay as well as scientific pubhc the impression that, as judged by 

 the results in other forms, as well as by the observations already made 

 at Hiroshima, the genetic effects of radiation would in practice be negli- 

 gible in human populations. 



The Way in Which an Increase in Mutation Rate Will 

 Affect a Population 



In considering this matter, a simple and cardinal point to be reckoned 

 with is that each mutation received by an offspring results, on the aver- 

 age, in the genetic death of one descendant genome or individual, no 

 matter how slightly detrimental the effect of the mutant gene may be 

 [Muller (49, 50, 51, 52, 54)]. This paradoxical result is a consequence 

 of the fact that the less detrimental genes will tend to accumulate so 



* Results reported by the Russells since the above was written, and now in press 

 in the 1951 Cold Spring Harbor Symposium Quant. Biol, have given definite evidence 

 that the per locus mutation rate induced by a given dose of x-radiation in mice is 

 far higher than in Drosophila, perhaps by as much as one order of magnitude. 



