THE PRODUCTION OF CHROMOSOME BREAKAGE BY IONIZING RADIATIONS 



energy available for transfer to chromosomal substances. Thus bacteria 

 irradiated in water and in broth have different survival rates even though 

 the oxygen tension in the cells may be similar. So far as breakage in 

 Tradescantia is concerned, it is likely that this is an important step because 

 it is here that the relative amounts of direct versus indirect energy are 

 determined. 



IRRADIATION 



PHASE I 



\ 



INDIRECT 



ENERGY 



TRANSFER 



DIRECT 



ENERGY 



TRANSFER 



I 



/ 



/ 



PHASE n 



SPECTRUM OF CHROMOSOMAL DAMAGE 

 INCREASING DAMAGE 



Figure 2. A schematic representation in more general form of the possible roles of radiation and oxygen 

 tension in inducing chromosomal aberrations. {Prepared in collaboration with Dr. K. G. Liining, 

 Institute of Genetics, University of Stockholm, and published with his kind permission.) 



(2) Phase //^Several steps can be involved here, but at present there is 

 no way of disdnguishing between them experimentally. Oxygen, through 

 the medium of indirect energy transfer, can contribute to the spectrum of 

 chromosomal damage, or it can enhance the damage already induced by 

 direct ionization. Anoxia, therefore, would tend to repair damage created 

 by direct energy transfer or to lessen the amount of damage created by 



260 



