Fig. 6. PCC analysis of MMC-treated human lymphocytes. (A-E) Sections of PCC spreads of MMC-treated G₁ human lymphocytes after in situ hybridization using whole chromosome-specific probes for chromosome 8 (green) and 9 (red) together with band-specific probes 8p11.2 and 9q12-13 in reversed colors. Colocalization of the chromosome 9 homologues was observed at the position of the heterochromatic bands (A) or at other part of chromosome 9 sometimes leading to a partial alignment (B,C). Also, chromosome breakage within the green-painted heterochromatic band (D) or in an arm of chromosome 9 (E) was frequently observed. (F) The induced colocalization of homologous chromosomes 8 or 9, or breaks in these chromosomes in G₁ human lymphocytes after treatment with 4 µM MMC for 1 hour (background frequencies are deduced). The induced colocalization and breaks were significantly different (P<0.01, Wilson's method) between chromosomes 8 and 9.