The staining of metaphase spreads for the quantification of SCEs was adapted from published protocols34,35. A 50 mg BrdU slow-release pellet (Innovative Research of America) was surgically implanted subcutaneously into 8-to-12-week-old mice. Unchallenged mice were injected with colchicine 24 h later and metaphases were prepared after 30 min. Mice challenged with ethanol were injected intraperitoneally with ethanol 8 h and 12 h after implantation of the BrdU pellet. A total ethanol dose of 5.8 g kg−1 was split between these two doses as described previously. Metaphases were prepared as outlined above. Cells were then dropped from a height of 30 cm onto chilled, humidified slides. The slides were then dried for 1 h at 62 °C in a hybridization oven. Cells were washed in 2× SSC for 5 min at room temperature. Cells were stained for 15 min at room temperature with 1 μg ml−1 Hoechst 33258 pentahydrate (H3569, Molecular Probes) in 2× SSC. The slides were then transferred to a Petri dish with 2× SSC and exposed to UV irradiation for 30 min in a Stratalinker Crosslinker (Stratagene). The
