Mitotic index is decreased to 0.41% in homozygous larval brains, compared to 0.94% in wild-type brains. More than 80% of metaphase figures in third instar mutant brains are abnormal, with the phenotypes falling in to two types; most metaphase figures have a pulverised appearance, being highly reminiscent of prematurely condensed chromosomes, while a smaller fraction have normally condensed figures containing chromosome breaks and show precocious sister chromatid separation. More than 50% of mutant anaphases have defects in chromosome segregation (chromosomal bridges or lagging chromosomes). Micronuclei are also seen.

Polytene chromosomes in salivary glands in homozygous third instar larvae are substantially underreplicated and show very little evidence of banding.

Homozygous larval brains show very little incorporation of BrdU.

The brains of mutant larvae do not halt progression through the cell cycle in response to hydroxyurea, in contrast to wild type, as they do not show a reduction in mitotic index.

The brains of mutant larvae do not show a drop in mitotic index after treatment with either etoposide or UV irradiation, indicating a failure to arrest the cell cycle.

Caffeine has no effect on the mitotic index in mutant larval brain neuroblasts.

Mutant larval brain neuroblasts arrest in mitosis in response to treatment with colchicine, as occurs in wild type.

Sister chromatids are apparently separated in homozygous larvae.

Imaginal discs of homozygous larvae are missing or degenerate. Defects in the cell cycle: few or no dividing cells, affects chromosome condensation and arrest of the cell cycle at metaphase.

L3 larval/early pupal lethal discs missing abnormal mitoses Homozygous larvae contain rudimentary imaginal discs, but disc primordia do not grow during larval development; testes and ovaries smaller than normal and cell number in central nervous system reduced. Mutant gonads do not survive metamorphosis when implanted into wild-type larvae. Homozygous cuticular clones appear to develop normally. Mutant larvae support growth of implanted wild-type discs. Normal gene product postulated to be required for cell proliferation; survival of somatic epidermal clones attributed to perdurance. Larval ganglia exhibit extremely low mitotic index; chromosomes irregularly condensed; extensive chromosome fragmentation observed frequently (Gatti and Baker, 1989);