a, Left, representative images of bone marrow metaphase spreads from wild-type mice treated with mitomycin C (MMC); n shows the number of SCE events per metaphase. Right, comparison between number of SCEs in the bone marrow of wild-type and Aldh2−/− mice treated with ethanol (5.8 g kg−1) or MMC (1 mg kg−1). Triplicate experiments, 25 metaphases per mouse, n = 75; P calculated by two-sided Mann–Whitney test; data shown as mean and s.e.m. Ethanol causes a strong homologous recombination response in Aldh2−/− mice, comparable to that observed in wild-type mice exposed to MMC. b, Left, representative images of bone marrow metaphase spreads from wild-type and Fanca−/− mice; n shows the number of SCE events per metaphase. Right, quantification of SCEs (duplicate experiments, 25 metaphases per mouse, n = 50; P calculated by two-sided Mann–Whitney test; data shown as mean and s.e.m.). Mice deficient in cross-link repair (Fanca−/−, or Fancd2−/− in Fig. 1a) show a small but significant increase in the number of spontaneous SCE events, indicating that a homologous recombination repair response occurs in the absence of the Fanconi anaemia pathway. c, Scheme depicting the formation of micronucleated erythrocytes. Micronuclei (Mn) generated by fragmentation or mis-segregation of chromosomes during erythrocyte maturation remain in the erythrocyte after extrusion of the main nucleus. These fragments can be detected by a DNA stain (PI+). During maturation, red-cell progenitors lose CD71 expression. Therefore, peripheral CD71+ red cells represent immature, short-lived reticulocytes (Ret) and CD71− cells represent mature, long-lived normochromic erythrocytes (NCEs). d, Proof-of-principle experiment showing the induction of micronucleated reticulocytes 48 h after MMC treatment (1 mg kg−1). P calculated by two-sided Mann–Whitney test; data shown as mean and s.e.m.; n = 29, 8, 20 and 9 mice, left to right. e, Treatment of Aldh2−/− mice with ethanol (5.8 g kg−1) leads to potent micronucleus formation. This induction is comparable to that observed in wild-type mice that were treated with the aneugen vincristine (Vcn, 0.2 mg kg−1, 48 h) or clastogenic γ-irradiation (IR, 400 rad, 48 h)46. P calculated by two-sided Mann–Whitney test; data shown as mean and s.e.m.; n = 29, 15, 10, 11, 25 and 15 mice. f, List of chromosomal aberrations observed in the bone marrow of 8-to-12-week-old untreated Aldh2−/−Fancd2−/− and control mice. g, List of chromosomal aberrations observed in the bone marrow of 8-to-12-week-old Aldh2−/−Fancd2−/− and control mice 48 h after ethanol treatment (5.8 g kg−1, injected intraperitoneally, IP). In f and g, three mice and 30 metaphases per mouse were analysed per condition, and the numbers represent the fraction of abnormal metaphases per mouse. h, Bar chart classifying the type of aberrations for each genotype (90 metaphases per condition). i, Examples of different types of chromosomal aberrations.