fzo¹/fzo² spermatids arrest development at mid-elongation with undifferentiated nuclei. However, caspase activation, only seen in wild-type cysts at the individualisation stage, still occurs.

Mitochondria in early spermatids of fzo¹/fzo² or fzo²/Df(3R)P2O males aggregate and form misshapen Nebenkerns. The mitochondria fail to fuse into two giant mitochondria as in wild-type males, instead many smaller mitochondria appear to wrap around each other at the onion stage. The mitochondria do unfurl and elongate in early elongation stage spermatids, although the mitochondria appear fragmented compared to wild-type. At later stages, each spermatid has many elongating mitochondria, rather than the normal two elongating mitochondrial derivatives.