332 GENE MUTATIONS CAUSED BY RADIATION 



Sax: 



We have done similar experiments and find that the effects of continuous 

 radiation are not cumulative. Chromosome aberrations increase for several 

 weeks, and then the frequency remains stationary even when radiation is con- 

 tinued for months. 



Muller: 



Back mutations, both spontaneous and radiation-induced, have been studied. 

 The likelihood of recovery for gene mutations is negligible. It is emphasized 

 that natural selection is operating on the somatic cells as well as on the gonadal 

 cells where chromosome aberrations are concerned. That is, damaged somatic 

 cells die out and the undamaged normal cells survive. But this effect is prac- 

 tically absent for gene mutations. 



