Drosophila Mitotic Genes Figure 3. RNAi phenotypes elicited by the genes detected in the screen (SA, SC and CY phenoclusters). Colors refer to the strength of the phenotype: pale blue, weak; blue, strong. The numbers in the CAB column are frequencies of chromosome aberrations per cell. The other numbers refer to relatively rare phenotypic traits. PHC, phenocluster: SA, spindle assembly; SC, spindle assembly and chromosome condensation; CY, cytokinesis. See legend of Figure 2 for main phenotypic traits. Other phenotypic traits: (1) long astral MTs in telophase; (2) drastic undercondensation of the heterochromatic regions of the chromosomes; (3) disorganized spindles; (4): split spindle poles; (5) multipolar spindles; (6) umbrella-like telophase spindles with all chromosomes at the astral pole; (7) centrosomes/asters detached from the spindle poles; (8) early cytokinesis defects: central spindle and contractile ring are both abnormal; (9) late cytokinesis defects: central spindle and contractile ring are normally assembled. doi:10.1371/journal.pgen.1000126.g003 as cell depleted for their products do not exhibit defects in late prophase/early prometaphase spindles. However, metaphase and ana/telophase spindles are often highly abnormal with respect to spindle morphology and the distribution of chromosomes along the spindle. The genes required for chromosome segregation (CS) can be subdivided into five phenoclusters (CS1, CS2, CS3, CS4 and CS5) based upon differences and similarities in the RNAi phenotypes (Figure 2). The CS1 group includes only the doubleparked (dup) gene. In most dup RNAi metaphase-like figures, the chromosomes are not replicated and have the appearance of single chromatid (Figure 5B). This is likely to results in a merotelic attachment of the spindle fibers to the kinetochore, leading to an impairment of chromosome movement during anaphase (Figure 5B). This phenotype has been previously observed in PLoS Genetics | www.plosgenetics.org 5 July 2008 | Volume 4 | Issue 7 | e1000126