There is a 5.5 fold increase in the percentage of mitotic cells in the mutant larval brain compared to wild type. Anaphase and telophase figures are not seen. There are a few prophase nuclei. A large number of metaphase-like figures are seen (87% compared to 14% in wild type), which includes defective metaphase figures. The mitotic chromosomes are abnormally condensed, with three classes of defects based on severity; 13% (Class I) have mild defects such as undercondensed chromosome arms and in some cases elongated centromeres. In 68% (Class II), mutant centromeres cannot be distinguished and chromosome arms appear shorter and thicker than in Class I. In addition, sister chromatid cohesion is often lost and the chromosomes have extremely aberrant morphology. 19% (Class III) have underwound centromeres and chromosome arms are decondensed and noticeably shorter than normal, having a "dumb-bell" morphology. Sister chromatid cohesion is almost always lost in these cases. Extensive chromosome fragmentation is seen. Mutants lack imaginal discs at the larval stage.