BrdU incorporation in third larval instar brains is reduced in homozygotes compared to heterozygotes. There is a 5.0 fold increase in the percentage of mitotic cells in the mutant larval brain compared to wild type. Anaphase, telophase and prophase figures are not seen, instead 100% of figures appear arrested in a metaphase-like state. A large number of metaphase-like figures are seen in which a highly condensed chromosome mass is present. Abnormal mitotic spindles are seen that are either anastral or have poorly focused poles. 49% of figures (Class I) have chromosomes aggregated at the metaphase plate, while 51% (Class II) have chromosomes scattered along the metaphase-like spindle. The spindle is diffuse but more focused than in Class I. The mitotic chromosomes are abnormally condensed, with three classes of defects based on severity, in third instar larvae; 5% (Class I) have mild defects such as undercondensed chromosome arms. In 85% (Class II), mutant centromeres cannot be distinguished and chromosome arms are decondensed. In addition, sister chromatid cohesion is often lost. 10% (Class III) have underwound centromeres and chromosome arms are more decondensed than in Class II, having a "dumb-bell" morphology.
Pupal tissues disintegrate, leaving empty pupal cases. Dissected third instar larvae have no imaginal discs and the CNS is reduced in size. esg and sna staining reveals absence of the imaginal discs is due to failure of proliferation. In larvae BrdU incorporation indicates the cell cycle is either prolonged or blocked after the first division(s).