CHROMOSOME ABERRATIONS IN ANIMALS 



681 



Table 9-10. Distribution among the Chromosomes of Breaks Utilized in 



3-break Rearrangements 

 (Bauer, 1939b) 



x 2 = 0.005 N = 1 P = ca. 0.95 



Table 9-11. Distribution of Breaks Utilized in 4-break Rearrangements 



(Kaufmann, 1946a) 



heterochromatin may be able to initiate the production of rearrangements 

 somewhat sooner than breaks in euchromatin. 



4. DIFFERENCES IN SENSITIVITY TO IONIZING RADIATIONS 



On the basis of the more general considerations of the process of 

 induced structural rearrangement outlined in the preceding pages, some 

 attention can be given to the factors responsible for differences in sensi- 

 tivity of cells to ionizing radiations. 



It has been recognized since the early years of the century that the 

 X-ray sensitivity of a tissue is related to its reproductive capacity 

 (Bergonie and Tribondeau, 1906). It has also been reported that cells 

 with a short mitotic cycle and intermitotic period are more sensitive to 

 radiation and suffer greater damage than those with a longer cycle 

 (Roller, 1947; Knowlton and Widner, 1950). Since high reproductive 



