ANALYSIS OF NATURALLY-OCCURRING AND RADIATION-INDUCED BREAKPOINT LOCATIONS IN HUMAN CHROMOSOME-1, CHROMOSOME-2 AND CHROMOSOME-4

The locations of observed breaks in three pairs of painted chromosomes from radiation-exposed and unexposed human peripheral blood lymphocyt es are described. No difference in the observed breakpoint locations w as seen from people exposed at Chernobyl, from healthy controls or fro m blood exposed to 2 Gy Cs-137 in vitro. However, the distribution of observed breaks within the painted chromosomes was not random. Fewer b reaks and rearrangements were observed near the ends of the chromosome arms. Three explanations for these findings were considered: cell sel ection, non-random efficiency of detection and non-random breakage or repair. Cell selection does not appear to be plausible because the dis tribution of observed breaks induced in vitro is not different from th ose induced in vivo. Non-random efficiency of detection is not