12% of homozygotes die as embryos, while the majority of homozygotes die as first instar larvae. Most of the mutant larvae die within 24 hours of hatching. Those that survive longer never progress beyond the first larval instar (as shown by their small size and mouth hook morphology). Muscle contractions are slower in Zasp^Δ larvae compared to wild type.

43% of Zasp^Δ/Df(2R)Jp1 animals die as embryos, while the majority die as first instar larvae.

Late stage 17 Zasp^Δ embryos lack the typical striated muscle pattern, indicating a Z line defect.

In freshly hatched Zasp^Δ larvae, Z lines are either completely absent or are severely disorganised and irregularly spaced in ultrastructural analysis of the muscles. The filaments of the muscles are also disorganised and are no longer arranged in parallel arrays.

Muscle detachment defects are seen from stage 16 onwards in Zasp^Δ embryos; the muscle fibers detach from myotendinous junctions. Some muscles are missing in some segments. Late stage 17 embryos occasionally show severe muscle detachment and rounding up of muscles. The muscle detachment is progressive (12% of embryos have rounded muscles at stage 17, but 98% of unhatched embryos have rounded muscles when analysed 24 hours later).

Zasp[+]/Zasp52^Δ is an enhancer of presumptive embryonic/larval muscle system phenotype of if^SEF