Embryos derived from mutant females show defects at the syncytial stage; there are frequent anaphase bridges, asynchronous mitoses and gaps in the normally uniform monolayer of nuclei.

Mutants appear to be defective in the synthesis-dependent strand annealing pathway; in assays of excision and repair of the P{hsw^a} element, the frequency of aberrant repair products is increased in mus309^unspecified flies compared to wild type (excision and repair events of P{hsw^a} in developing mitotic germ line cells of mus309^unspecified males carrying P{hsw^a} and a source of transposase can be detected by crossing the males to females homozygous for P{hsw^a}. The female progeny have 3 classes of eye colour; 85.9% have apricot-coloured eyes (these are probably derived from cells in which P{hsw^a} did not excise, but some may have resulted from excision followed by repair to restore the complete P{hsw^a} element). 0.1% have flat red eyes (more than 90% of the red eyed flies have a single LTR remaining at the copia insertion site in the transgene). 14.0% have yellow eyes, corresponding to aberrant repair events that result in the loss of w activity).