Hemizygous or homozygous Top1⁷⁷ embryos survive until larval stages, and appear to have normal nuclear morphology. However necrotic tissues are observed throughout the body of some second instar larvae. The imaginal discs in mutant larvae often fail to develop at all. In those that do, they either degenerate or are smaller than wild-type. Top1⁷⁷/Y, Top1^hs.2 adult males (maintained without heatshock) are fertile and their there testes have no gross defects when compared to wild-type. Top1⁷⁷, Top1^hs.2 adult females (maintained without heatshock) are sterile and lay very few eggs. A wide range of defects are observed as early as in the germarium and as late as matured oocytes. In a mutant germarium, no regional development of cysts can be clearly ascertained and the abnormal nuclear morphology reveals extensive nuclear lysis. About 20-40 extra nurse cells are seen in post germarial egg chambers, and multiple oocyte-like cells are also seen, although anterior posterior polarity appears to be set up normally. The morphology of the nurse cell nucleus is also apparently normal as compared to wild-type. The follicle cells also appear to be underreplicated. Most mutant egg chambers are degraded during oogenesis, but a few do survive to complete vitellogenesis and develop a chorion. No defects in follicle cell migration are seen, however they are fewer than normal and irregularly distributed over the mature oocyte. The dorsal appendages are shorter than wild-type. the embryos laid by Top1⁷⁷, Top1^hs.2 adult females exhibit various nuclear defects. Multiple layers of nuclei beneath the cortex are seen, nuclear division cycles are prolonged and the normal synchronicity of these cell divisions has been disrupted. Chromosome condensations and segregation are also defective.

Females heterozygous for Top1⁷⁷ may show increased frequencies of non-disjunction.