XXXIX 



RADIATION AND THE STUDY OF MUTATION IN ANIMALS 



Jack Schultz 



Carnegie Institution of Washington, William G. Kerckhoff Laboratories 

 of the Biological Sciences, California Institute of Technology, Pasadena, 



California 



Introduction. The discovery of the effect. The quantitative study of mutation. 

 The characteristics of the mutation process: The diversity of mutation rales at different 

 loci — The stability of different members of allelomorphic series — The localized occurrence 

 of the mutation process — Chromosome breakage and the production of mutation— The 

 "group effect," the association of mutations ivith each other. The studies of general 

 mutation rate: The relations between lethal anil viable mutations — The variability of 

 lethal mutation rate — Mutation rate in different tissues. The mode of action of radiation: 

 General considerations — The relation between intensity and mutational effect — The 

 relative effectiveness of different wave-lengths — The time factor, secondary reactions — 

 Induced changes of susceptibility to irradiation — The question of direct effects. The 

 causes of "spontaneous" mutation. The nature of the mutation process. References. 



INTRODUCTION 



The chief interest in the experimental production of mutations lies 

 in the possibility of studying the nature of the mutation process and, by 

 extension, of the gene itself. Of the many environmental agents tested, 

 by far the most effective turns out to be short-wave radiation. Hence 

 at the outset a double problem is presented. The effects of short-wave 

 radiation on biochemical systems are comparatively little understood; 

 accordingly there exists no extensive basis from which inferences as to 

 the behavior of more complex systems may be drawn. From the opposite 

 point of view, the effects of short-wave radiation in the production of 

 mutations are apt to be instructive. Genes are at present the elementary 

 biological units; a knowledge of their properties and behavior must 

 necessarily have repercussions on many other fields of biology. For 

 example, it is not difficult to see in the grosser effects of radiation on cell 

 division the results of primary effects on the genes or chromosomes. 



The first conclusive evidence for the production of mutations in 

 animals by X-rays was presented by Muller (104) in 1927. In the rela- 

 tively short time since then a large body of data has been accumulated 

 and the field clearly outlined. Two general questions have been raised, 

 and it is with the attempts to define and answer them that this review is 

 concerned. The first involves solely the biology of the mutation process: 

 what are its characteristics, now at last to be seen in semiquantitative 



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