Drosophila Mitotic Genes Figure 4. Genes required for the maintenance of chromosome integrity. (A) Examples of chromosome aberrations in colchicine/hypotonic- treated cells. Arrows and arrowheads point to chromatid and isochromatid deletions, respectively. Asterisks indicate asymmetric (U-type; one asterisk) and symmetric (X-type; two asterisks) chromatid exchanges. (B) Mitotic cells with acentric chromosome fragments (arrowheads) that have migrated to the cell poles. Staining for Cenp-C shows that the fragment at the pole of the RnrS-depleted metaphase (arrowhead) lacks the kinetochore (see text for further explanation). meta, metaphase; telo, telophase. In the merged figures, DNA is blue, Cenp-C red, and tubulin green. Scale bars, 5 mm. (C) The 44 genes required for chromosome integrity. Colors in the CAB (chromosome aberrations)/cell column denote the strength of the phenotype: light blue, weak; blue, strong. Numbers in this column are the frequencies of CABs per cell (see Methods for details). In control cells, the frequency of spontaneous chromosome aberrations is 0.2460.014 per cell (n = 941; from 12 independent experiments). doi:10.1371/journal.pgen.1000126.g004 PLoS Genetics | www.plosgenetics.org 6 July 2008 | Volume 4 | Issue 7 | e1000126