680 



RADIATION BIOLOGY 



tion, as is illustrated by the data of Kaufmann (1946a) presented in 

 Table 9-11. 



The low incidence of rearrangements of each of the complex types 

 involving five or more breaks precludes their analysis on a similar basis, 

 although Fano (1943b) and Kaufmann (1943) have shown that a con- 

 centration of the breaks in one or two limbs often occurs in these multiple- 

 break rearrangements. Fano suggested that in the recombination proc- 



Table 9-9. Frequency of X-chromosome Inversions (X/X) and of Trans- 

 locations BETWEEN THE X AND THE AUTOSOMES (X/A) 

 (Data listed in first four lines involve only breaks in divisions 1-19, data in fifth 

 line involve breaks in division 20. Expected values are calculated on basis of random 

 recombination among five long limbs.) 



(Kaufmann, 1946a) 



° From nuclei having only one inversion or one translocation. 

 b From more complex rearrangements in addition to 2-break rearrangements. 

 c Regions included are IF, 3C, 4A, 4E, 7B, 9A, 11 A, 12D, 12E, 16F, 19E. 

 d X-chromosome breaks in subdivisions not listed in preceding line. 



ess adjustments among the chromosomes originally involved may cause 

 mechanical disturbances of sufficient intensity to produce new breaks, 

 which then participate in the development of the complex rearrangement. 

 Another possibility, which does not require the participation of mechan- 

 ically induced breaks, is that heterochromatic breaks initiate the process 

 of recombination on an intrabrachial level, and the developing rearrange- 

 ment then incorporates adjacent potential breaks. This alternative is 

 based on the suggestion of Kaufmann (1946a) that potential breaks in 



