Natural and Induced Chromosomal Changes 



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which time their energy is absorbed. Energy 

 is transferred into ionization when some of 

 these rays are stopped by an atom which sub- 

 sequently loses an orbital electron. This 

 electron, torn free of the atom, shoots off at 

 great speed and can, in turn, cause other 

 atoms to lose electrons in a similar manner. 

 All atoms losing electrons become positively 

 charged ions. The freed electrons are finally 

 captured by other atoms which become nega- 

 tively charged, or negatively charged ions. 

 Since each electron lost from one atom is 

 eventually gained by another atom, ions oc- 

 cur as pairs. In this way a track of ionizations 

 is produced which often has smaller side 

 branches. The length of a primary track and 

 its side branches, and the density of ion pairs 

 within these, will differ depending upon the 

 type and energy of radiation involved. Suf- 

 fice it to say that all known ionizing radia- 



FIGURE 21-4. Structural changes X-ray-induced {75-150 r) in normal human male fibroblast-like 

 cells in vitro. Arrows show: {A) broken chromosomes, (B) translocation (center) and dicentric (lower 

 left), (C) ring chromosomes. A, B are in metaphase (see Fig. 18-9), C is late prophase. (Courtesy 

 ofT. T. Puck, Proc. Nat. Acad. Sci., U.S., 44:776-778, 1958.) 



