Homozygotes die as first to second instar larvae. Homozygous larvae are less active than wild-type larvae, have slow muscle contractions and appear uncoordinated. nab^e310/Df(3L)GN19 animals die during the first to second larval instars. The larvae initiate fewer movements than normal and have slow muscle contractions. nab^e310/nab^A23 animals survive larval development, and most of them pupate. Most of the pupae eclose, although about 20% are unable to completely escape the pupal case and become trapped. The eclosed adults appear morphologically normal and show grooming behaviour. However, when they try to walk they are extremely uncoordinated and fall often, and if they land on their backs, a few of the adults are able to right themselves with considerable difficulty. The adults do not fly or jump and die within 24-48 hours of eclosion, presumably from an inability to feed. nab^e310/nab^G26 animals generally die during the first to second larval instar, although about 5% pupate. These pupae appear morphologically normal when examined outside the pupal case, but they never eclose, although weak movements are seen. Homozygous embryos lack 1-4 EL (eve lateral) neurons in a subset of abdominal segments. The mean number of EL neurons per abdominal hemisegment is 7.1 in homozygous embryos compared to 8.1 in wild-type embryos, and the number of abdominal hemisegments with less than 7 EL neurons is 18.34% in homozygous embryos, compared to 7.68% in wild-type embryos. Glia appear to develop in normal numbers and migrate appropriately to form the longitudinal glial array and exit glia in homozygous embryos. Homozygous clones fail to form in the eye, either in a wild-type background or a Minute background.