198 



Cellular Events Produced by Ionizing Radiations / 1 : 5 



neurospera, mice, and man is increased by exposure to ionizing radi- 

 ations. This produces breaks in the chromosomes which come together 



hV VWWVWAAA*- 



Centromere 



/ 



Normal 



Broken 



Double stranded 

 (Prophase) 



Lost as Dicentric - Prevents 



No Completion of 



Centromere Telophase Cell 

 Division 



(a) Break in one chromosome 

 prior to division 



Normal WWWWWW, -#- 



Two 

 Breaks 



Translocation 



Jmv- 



Alternate 

 Translocation 



-ANv- 



Lost 



■^ W*/WV -#- 



-—o 



-r 





-#. WWWW- 



Dicentric 



(b) Translocation due to one break 

 in each of two chromosomes 



JVWWWWVWWW 



-V wwvwwv 



Normal 



Two 

 Breaks 



J VWA — o 

 Lost 



o 



Centric Ring 

 Chromosome 



-VWVWWWW^ 



-w vww 



VWWWV — O {^J 



Centric Chromosome [_ os f 



Ring 



(c) Two breaks forming ring chromosome 



VWWWVW>- 



VWWVW*- 



V — wvwwww- 



Normal 

 Two Breaks 

 Inversion 



(d) Two breaks forming inversion 



Figure 8. Breaks in chromosomes. Shapes are diagrammatic 

 only and have no physical significance. Broken ends are not 

 similar to normal chromosome ends but act sticky. They tend 

 to recombine with other broken ends. The site of the break 

 is always altered no matter how recombination occurs. After 

 H.J. Mueller, Chapter 7 in Radiation Biology, Vol. 1, Part 1, 

 A. Hollaender, ed., (New York: McGraw-Hill Book Company, 

 Inc., 1954). 



(recombine) in many fashions, some very bizarre. Some types of 

 breaks observed with fruit flies are shown in Figure 8. Ionizing radiations 

 may also damage or alter chromosomes without actually breaking them. 



