sparrow: cytogenetic effects of ionizing radiations 



89 





 



100 

 10 



200 

 20 



DOSAGE 



300 

 30 



400 r (XRAY) 

 40 n (NEUTRONS) 



Figure 10.— Relation between frequencies of chromosome interchange 

 (dicentric and centric rings) and dosages of fast neutrons and X-rays. 

 1 n unit = ca. 2.5 r. After Giles (49). 



VII. Nature of Mutational Events Induced 

 by Ionizing Radiation 



The relationship between the frequency of induced mutations 

 and the amount of ionizing radiation depends in part upon the nature 

 of the mutational event. Phenotypic change which results from 

 chromosomal breakage, or the resultant aberrations, will have the 

 same dosage response curves as the breakage or aberration event or 

 events which caused it. For instance, simple one-hit deletions (of 

 markers) will show a linear increase with increasing dose, whereas 

 losses resulting from two-hit deletions will have a dosage response 

 curve which is nonlinear and will approach the dose-squared 

 relationship at high dosages or high intensities (163). 



It has been shown in a wide variety of organisms that point 

 mutations increase linearly with increasing dose (Figure 11) and are 

 generally independent of intensity (108). Occasional departures from 

 linearity are found (see 110), but in this case it has been suggested 



