Neuroblasts in Zw10⁵ mutant brains exhibit chromosome nondisjunction, but the brains do not display a premature neuroblast loss phenotype.

Mutant spermatocytes have less numerous Golgi structures (~10/cell) than in wild type (~20/cell), and exhibit severe morphological defects.

Spermatids from mutant third instar larvae testes are multinucleated (with nuclei of variable size) and have a single large nebenkern, indicating defects in chromosome segregation and cytokinesis.

The overall structure of the endoplasmic reticulum is not grossly affected in mit(1)15⁵ mutant spermatocytes, except very late in meiosis as a secondary consequence of incomplete cytokinesis.

Mutant spermatocytes display normal contractile rings during late anaphase, but these fail to constrict during mid-telophase and appear fragmented by late telophase. Similarly, the central spindle is regular during anaphase and early telophase, but appears less dense and irregularly shaped in late telophase. Furrow ingression is only partial in many mutant cells, and the furrow eventually regresses. In these cases, the increase in cell perimeter during cytokinesis is substantially lower than in wild type. Fusion of Golgi-derived vesicles with the furrow membrane appears normal.

The acroblast of mit(1)15⁵ spermatids consistently appears as an aggregate of multiple unfused vesicles, rather than a continuous structure as in wild type.

Brain cells are hyperploid. Aneuploidy involves improper chromosome segregation at anaphase: precocious sister chromatid separation. Mitotic index and the ratio of numbers of cells in anaphase relative to the total number of mitotic figures in larval brains is similar in wild type. Lethal phenotype can be rescued by P element mediated transformation of a wild type mit(1)15 gene copy.

A high frequency of larval neuroblasts are aneuploid.

Males and homozygous females are semi-lethal. Surviving flies have reduced rough eyes, bristles on the thorax and head are sometimes missing, wings are abnormal with a thin texture and thickened veins.

Semilethality is polyphasic, occurs during larval, pupal and adult stages. Growth rate of individuals slows during the second larval instar, puparium formation is delayed. Mosaic analysis demonstrates mutant phenotype is non-autonomous. Surviving males have rough reduced eyes, wings have thickened veins and incisions on the inner margin. Thoracic hairs are irregularly arranged, dorsocentral, scutellar, ocellar, orbital and vertical bristles are frequently absent. Sperm are immotile.