Cbx1^−/− neurospheres exhibit an increased genomic instability. (A) A mitotic chromosome spread showing the normal situation in which sister chromatids are paired. (B–E) Chromosomes from the Cbx1^−/− neurosphere cells exhibit a variety of aberrations, including unpaired sister chromatids that have undergone PCD (B, arrow), increased ploidy (C), diplochromosomes (D, arrow), and micronuclei (E). Telomeres (red signals) in all panels were labeled by a specific PNA probe. (F) The table shows that there is a highly significant increase (P < 0.001) in PCD, polyploidy, diplochromosomes, and micronuclei between Cbx1^−/− and the other two genotypes (Cbx1^+/− and Cbx1^+/+). There is only a borderline significant difference between Cbx1^+/− and Cbx1^+/+. Bars, 5 μm.