CHAPTER 8 



The Manner of Production of Mutations by Radiation 



H. J. MULLER 



Department of Zoology, Indiana University 



"Point-mutation" Jrequency in relation to amount and distribution of ionizations. 

 Chromosome breakage and gross rearrangement frequency in relation to amount and dis- 

 tribution of ionizations. Number of ionizations necessary for breakage. Production of 

 minute structural changes by ionizing radiation. Possible relations between point muta- 

 tions and breaks produced by radiation. Larger scale evidence of spatial limitation in 

 mutagenesis by ionizing radiation. Evidence of time limitation in mutagenesis by ioniz- 

 ing radiation. Spatial limitation as evidenced by the effects of ion distribution. The 

 target hypothesis as applied to mutagenesis. Production of point mutations and chromo- 

 some changes by ultraviolet. Point mutations in relation to quantity and quality of 

 ultraviolet. Repair and enhancement in ultraviolet mutagenesis. Mutagenesis by 

 ultraviolet treatment of the medium. Influence of biologically determined conditions on 

 high-energy mutagenesis. Influence of water and oxygen on high-energy mutagenesis. 

 Influence of temperature, infrared, and other physical factors on high-energy mutagenesis. 

 Other chemical influences on high-energy mutagenesis. Mutagenesis by cosmic and other 

 natural radiation. Nuclear transmutation and other physical influences as mutagens. 

 Questions concerning selectivity of radiation mutagenesis. Concluding considerations. 

 References. 



In this chapter it is assumed that the reader is already famihar with the 

 facts set forth in Chap. 7, concerning the kinds of primary genetic effects 

 produced by radiation and the ways in which these result in further 

 changes that affect subsequent generations of cells and of individuals. 

 Attention is here focused on the findings concerning the manner in 

 which the primary effects of the two major kinds, gene mutations and 

 chromosome breaks, are produced and the conditions affecting their 

 production. 



1. "POINT-MUTATION" FREQUENCY IN RELATION TO 

 AMOUNT AND DISTRIBUTION OF IONIZATIONS 



One of the most important findings concerning the manner of produc- 

 tion of "point mutations" by ionizing radiation is that, within the wide 

 range of dosage for which it has been possible to obtain statistically sig- 

 nificant evidence, their frequency varies in simple linear manner with the 



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