CHROMOSOME ANALYSIS BY FLUORESCENCE IN-SITU HYBRIDIZATION - FURTHER INDICATIONS FOR A NON-DNA-PROPORTIONAL INVOLVEMENT OF SINGLE CHROMOSOMES IN RADIATION-INDUCED STRUCTURAL-ABERRATIONS

The frequencies of symmetrical complete and incomplete translocations and dicentrics induced in human lymphocytes after in vitro irradiation with 3 Gy X-rays were analysed by the use of fluorescence in situ hyb ridization (FISH). Single whole chromosome painting (WCP) probes, spec ific for chromosomes 1-4, 6-10, 12, 14 and X were hybridized separatel y. A human pancentromeric DNA-probe was used simultaneously for unequi vocal centromere detection. For both aberration types, symmetrical tra nslocations and dicentrics, a significant deviation from a DNA-proport ional distribution was found. In general, chromosomes with a higher DN A content (chromosomes 1-3, 6 and 7) were less frequently involved in the formation of symmetrical translocations and dicentrics than expect ed according to their DNA-content, whereas smaller chromosomes were mo re frequently involved. The only exception was chromosome 4, exhibitin g the highest translocation frequency of all chromosomes analysed. Rat ios of the yields of symmetrical translocations to the yields of dicen trics varied between 0.9 and 1.8 for the single chromosomes. The prese nt results substantiate our previous data obtained with identical chro mosomes but examined in four different triple combinations.