Imprecise excision of the progenitor P{lacW}endosS067006 insertion.
Brains of homozygous larvae approximately half normal size. The mitotic index of mutant neuroblasts is almost double that of wild type and there is an increase in the ratio of metaphase:anaphase figures ( 11:1 compared to 4:1 in wild type). The mitotic chromosomes are undercondensed and there is a high incidence of chromatin bridges during anaphase.