Retinal sections reveal that ommatidia in hpo^MGH3 mutant clones have the normal complement and arrangement of photoreceptor cells but are separated by significantly more interommatial tissue. Additional layers interommatidial cells are apparent between ommatidia in mutant pupal retinas at 48 hours after puparium formation. At 38 hours APF, when excess interommatidial cells are eliminated by apoptosis, most of the cell death in discs containing hpo^MGH3 mutant clones is restricted to wild-type portions of the disc. Homozygous clones of hpo^MGH3 mutant cells in various imaginal discs, cause outgrowths of tissue. Portions of wings containing large hpo^MGH3 clones are larger than the corresponding portion of a wild-type wing. In hpo^MGH3 mosaic eye discs, the pattern of S phases is normal in the anterior portion of the disc and in the second mitotic wave (SMW) but in mutant portions these eye discs, S phase (BrdU-incorporating) nuclei can be seen posterior to the (SMW) and in the morphogenetic furrow (MF), a situation not seen in wild-type. i.e.- hpo^MGH3 cells continue to replicate their DNA when surrounding wild-type cells are arrested in G1. Mitotic cells occur in mutant clones many ommatidial rows posterior to the SMW, a region devoid of mitoses in wild-type eye discs.