Mutant mushroom body neuroblast clones show a reduced cell number and a "spotty axon" phenotype. Single cell mushroom body neuron clones examined in the adult show a twofold reduction in total dendritic length and branching points compared to wild type. Axon swellings occur in these cells preferentially at the distal ends of axon branches.

Homozygotes die during the late third larval instar stage. Homozygous larvae show a progressive posterior sluggish phenotype leading to complete posterior paralysis (the anterior of the larva remains noticeably mobile). There is a complete absence of imaginal tissue. Homozygous larval brains show a profound mitotic defect; there is a striking absence of prometaphase and metaphase mitotic figures. Only infrequent defective anaphase and telophase figures are seen. The few anaphase figures have severe bridging and lagging chromosomes. In addition, apparent telophase bridging in which DNA has become trapped between two dividing nuclei. Hemizygotes die as late pupae, and show posterior larval sluggishness, a peculiar tail flipping phenotype and accumulations of axonal cargo within their segmental nerves. The synaptic cargo tends to accumulate at the distal regions of axons with only infrequent proximal accumulations. The segmental nerves have swollen axons that have become filled with axonal cargo. These swollen axons are on average twice the diameter of the largest axon observed in wild type. Two classes of axonal accumulations are seen; small single component (small clear vesicles) accumulations and larger multi-component accumulations. Loss of axons and nerve degeneration is also seen. Hemizygotes that survive into late pupal stages have rough pupal eyes, missing bristles and the imaginal tissue is reduced in size. Larval brains have a significant number of mitotic defects; numerous polyploid mitotic figures are seen. Many of the polyploid figures show hypercondensation of the chromosomes. Abnormal anaphase figures are also seen with hypercondensed chromosomes and disorganisation of the chromosomes around the presumptive poles. Apparently normal mitotic figures are also seen. The mitotic index is fivefold higher than in wild type.