A search for radioresistance in experimental populations of Drosophila with radiation histories

Human lymphocytes in the G₀ stage were irradiated with UV light and X-rays. A 2-fold increase in the yield of dicentrics was observed in comparison with the yield for X-rays alone. This synergistic effect was constant irrespective of the variation in the UV dose between 50 and 100 erg/mm².The individual chromosomes participated in interchange aberrations as expected from a random distribution per mitotic chromosome length unit. This observation is in contrast with the recent finding that X-ray-induced chromosome-type breakage is preferentially located on chromosomes with relatively large amounts of R-bands. Thus, the present data indicate that the additional breakage points, due to the synergism, had a different distribution between chromosomes from those induced by X-irradiation alone. Mechanisms that could account for the synergistic reaction are discussed.