sparrow: cytogenetic effects of ionizing radiations 



85 



PHASE 



I 



PHASE 



n 



PHASE 



m 



PARTICLES WITHIN 

 TARGET VOLUME 



IRRADIATION 



TEMPERATURE 

 --OXYGEN — 



PARTICLES OUTSIDE 

 TARGET VOLUME 



(NOT WITH a PARTICLES) 



EFFECTS INSIDE 

 TARGET VOLUME 



EFFECTS OUTSIDE 

 TARGET VOLUME 



POTENTIAL BREAKS 



MODIFIERS 



PHYSIOLOGICAL VARIATION 



LATENT 

 PERIOD 



SEPARATION OF 

 BROKEN ENDS 



I 



I 



I ALTERED 



IPROBABILITY 



-T OF 



'SEPARATION 



(NUCLEOPROTEINS, VISCOSITY, ENZYMES, ETC ) 



CENTRIFUGE 

 ULTRASONICS 

 COLCHICINE 



VARIATIONS OF MECHANICAL CONDITIONS 

 (AND RATE OF REPAIR OF CHROMONEMATA P) 



PRIMARY BREAKS 



J , , i 



FAILURE 

 TO ADHERE 



HEALING 

 OF ENDS 



ADHESION OF 

 BROKEN ENDS 



OLD 

 WAY 



REPAIR OF 

 CHROMONEMATA 



RESTITUTION 



'STICKINESS' '.'CLUMPING' -EFFECTS -— 



ON RATE OF DIVISION OF NUCLEI / 



/ 

 / 

 ?/ 

 / 



-GENE MUTATION 



i 



OBSERVED 

 BREAKS 



OBSERVED 

 REUNIONS 



IMPAIRED CHROMOSOME 

 REPRODUCTION? 



Figure 7. — Suggested pathways of events concerned with the produc- 

 tion of chromosome aberrations and mutagenesis. After Thoday (188). 



to chromosome rupture and several possible hypotheses have been 

 proposed (3, 4, 23, 24, 79, 80, 177, 178, 185, 197, 198). Regardless of 

 the nature of the events which occur at the submicroscopic level, it is 

 now fairly clear that not only can chromatids be broken independent- 

 ly of each other but also that half chromatid or subchromatid break- 

 age can occur (39, 195). Since the potentialities for recombination 

 vary with the number of strands present and since the number of 

 strands varies with the stage of meiosis and mitosis, it is apparent that 

 the stage of cell division irradiated can have a great effect on the 

 outcome of the initial breakage events which occur (194). The num- 



