trrK662X mutant somatic clones show a growth advantage over the wild-type cells as the trrK662X mutant tissue is relatively overrepresented in the mosaic adult eyes. However, the overall size of the adult mosaic eyes or eyes composed almost entirely by the mutant cells (generated by mitotic recombination with a chromosome bearing a recessive cell-lethal mutation, thus removing the wild-type twin spots) is decreased. The trrK662X clones display a disrupted ommatidial lattice (misoriented ommatidia, missing photoreceptor cells), giving the mutant tissue a rough appearance. Extra inter-ommatidial cells are observed in trrK662X clones in the pupal retina. trrK662X mutant clones are overrepresented also in the third instar larval eye discs and induce increased apoptosis in the mosaic discs - at least some of the dying cells are wild-type.