EFFECT OF CHROMOSOME SIZE ON ABERRATION LEVELS CAUSED BY GAMMA-RADIATION AS DETECTED BY FLUORESCENCE IN-SITU HYBRIDIZATION

Fluorescence in situ hybridization (FISH) is a powerful technique for detecting genomic alterations at the chromosome level. To study the ef fect of chromosome size on aberration formation, we used FISH to detec t initial damage in individual prematurely condensed chromosomes (PCC) of gamma-irradiated G(0) human cells. A linear dose response for brea ks and a nonlinear dose response for exchanges was obtained using a ch romosome 1-specific probe. FISH detected more chromosome I breaks than expected from DNA based extrapolation of Giemsa stained PCC preparati ons. The discrepancy in the number of breaks detected by the two techn iques raised questions as to whether Giemsa staining and FISH differ i n their sensitivities for detecting breaks, or is chromosome 1 uniquel y sensitive to gamma-radiation. To address the question of technique s ensitivity, we determined total chromosome damage by FISH using a tota l genomic painting probe; the results obtained from Giemsa-staining an d FISH were nearly identical. To determine if chromosome 1 was uniquel y sensitive, we selected four different sized chromosomes for paint pr obes and scored them for gamma-ray induced aberrations. In these studi es the number of chromosome breaks per unit DNA increased linearly wit h an increase in the DNA content of the chromosomes. However, the numb er of exchanges per unit of DNA did not increase with an increase in c hromosome size. This suggests that chromosome size may influence the l evels of aberrations observed. Extrapolation from measurements of a si ngle chromosome's damage to the whole genome requires that the relativ e DNA content of the measured chromosome be considered.