CHAPTER 7 



The Nature of the Genetic Effects Produced by Radiation 



H. J. Mulleri 

 Department of Zoology, Indiana University 



Fundamental properties of the genetic material. Transmission of the genetic material. 

 Effects of radiation on the transmission of the genetic material: Interference with cell divi- 

 sion and induction of polyploidy — Disarrangement of cell division and induction of 

 aneuploidy involving ivhole chromosomes — Effects on crossing over. Consequences of the 

 production of a single chromosome break. Consequences of two breaks in separate 

 chromosomes. Consequences of two breaks in the same chromosome. Structural changes 

 of greater complexity. Nonrandom incidence of the changes produced by chromosome 

 breakage. Position effects induced by structural changes. Influence of stage of cell at 

 time of exposure on the consequences of chromosome breakage. Manner of incidence of 

 radiation-induced and spontaneous mutations of genes. Relative frequencies of different 

 types of character changes caused by radiation-induced and spontaneous mutations. 

 Effects of changing the relative quantities (dosage) of genes. Dominance. Radiation 

 and spontaneous gene-mutation frequencies in Drosophila. Differences between the 

 production of mutations in different species. Agents other than radiation which sepa- 

 rately affect mutation frequency. Influence of normal metabolic processes on the occur- 

 rence of gene mutations. Relation, between mutagenicity and carcinogenicity. Manner of 

 accumulation, expression, and elimination of mutations. Manner of incidence of radia- 

 tion damage to subsequent generations. Speeding up of evolution by irradiation. Practi- 

 cal applications of the action of radiation on the genetic material. Irradiation of the 

 genetic material as a means of biological investigation: Field of chromosome behavior and 

 properties — Field of gene properties and gene evolution — Fields of development, physiology, 

 pathology, and biochemistry. References. 



The gravity of the genetic effects of radiation is of a different order of 

 magnitude from that of all the other biological effects of this agent in that, 

 in the first place, the genetic effects are essentially irreparable. They are 

 therefore also, if repeated, cumulative over an unlimited period. In fact, 

 like all other genetic changes, they tend to be not merely persistent but 

 self-multiplying. They are, in different cases, of utterly diverse kinds, 

 and they range from the mildest to the most radical. The reasons for 



' The author wishes to express his grateful appreciation of the invaluable aid ren- 

 dered by Dr. Irwin H. Herskowitz in putting chaps. 7 and 8 into their present form and 

 preparing the literature lists. Grants received by the author from the Atomic Energy 

 Commission and the American Cancer Society, affording assistance for his research 

 in this field, make it possible for him to devote the time necessary to the preparation 

 of these chapters. 



351 



