REFERENCES 439 



gens required to double the natural rate of mutation per generation in 

 man is not as high as the 300 r estimated by Evans, and there is at 

 least one argument, that advanced bj^ Wright, for thinking that it may 

 be as low as 3 r. 



It would be out of place here to attempt to discuss all the published 

 calculations of the genetic hazards of radiation. The above examples 

 were chosen to illustrate some of the difficulties encountered and the 

 wide range of current estimates. It should be noted that the difficult 

 problem, mentioned earlier in this paper, of evaluating the effect of a 

 given increase in mutation rate was not considered here. The sole ob- 

 jective under discussion was an estimate of the increase in rate following 

 a given exposure to radiation. It has been shown that a wide range of 

 answers to this limited question is possible according to the interpreta- 

 tions placed on the available data which, at the present time, are com- 

 prised mainly of the induced and spontaneous mutation rates in Dro- 

 sophila together with the spontaneous rates of a few genes in man. It 

 is apparent that one of the pressing needs in the estimation of human 

 hazards is for basic information on mutation rates in mammals. 



REFERENCES 



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3. Deringer, M. K., W. E. Heston, and E. Lorenz, Biological effects of long- 

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7. Hertwig, P., Zwei subletale rezessive Mutationen in der Nachkommenschaft 

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