In the Chinese hamster genome,SINEs (short repetitive interspersed sequences, the major onebeing the Alu sequence family) and LINEs (long repetititive inter-spersed sequences) are partitioned in G-light (which represent theactive housekeeping subgenome) and G-dark (which pertain to themostly inactive tissue-specific subgenome) bands. This partition-ing allows specific targeting of DSB induced by AluI or BamHI tothe housekeeping and tissue-specific subgenomes respectively. Aco-localization of breakpoints was found with a preferential occur-rence (>70%) in G-light bands independent of the cell cycle stagein which aberration production took place. Similar results werefound with DNaseI and radiation, suggesting that active chromatinfrom G-light bands is more prone to damage.