Equal induction and persistence of chromosome aberrations involving chromosomes with heterogeneous lengths and gene densities

Little is known about the factors modulating the initial induction and persistence of chromosome aberrations. Chromosome length and gene density have been proposed to play a significant role. We have therefore analyzed the induction and persistence of γ-ray-induced aberrations involving four human chromosomes (1, 4, 18, and 19) with highly heterogeneous lengths and gene densities. Multicolor FISH was performed on a wild-type lymphoblastoid cell line 1, 3, 7, 14, 28, 42, and 56 d after γ-irradiation. The frequency of induced chromosomal aberrations was proportional to the length of the chromosomes. Complex aberrations, dicentrics, and fragments were highly unstable and disappeared during the first week after treatment and with similar kinetics for all four chromosomes. The frequency of translocations decreased with time and followed an exponential decline. Thirty percent of the γ-ray-induced translocations were stable over the entire study period, irrespective of the length and the gene density of the chromosome involved. Accordingly, we concluded that the induction of chromosome aberrations is proportional to the length of the chromosome, that gene density makes no measurable contribution to induction, and that neither length nor gene density influences the persistence of chromosome aberrations.