Homozygous clones in the eye disc undergo less than half as many mitoses as control clones. Dividing cells within the clone are usually next to the boundary with wild-type cells. BrdU incorporation is normal in mutant cells.
Heterozygotes have wild-type wings.
Germline clones reveal no requirement for spi in patterning the egg, or in the viability or patterning of the embryo.
In mutant eye clones the initial single neuron stage ommatidia appear normal, as do their spacing. However no further progression occurs, and the clusters appear to be arrested at the one neuron stage. The wave of DNA synthesis immediately following the furrow is unaffected in spi mutant clones. The early development of the preclusters is normal up until the 5-cell stage. Development proceeds normally anterior to and in the furrow (up to the specification and early differentiation of the founding R8 photoreceptor cells) but the specification of R2 and R5, and all subsequent steps, fail. Homozygous spi mutant clones are apparently equal in size to their homozygous wild-type twin-spots.
Retinal clones induced during first larval instar show defects in the formation of photoreceptor cells R8, R2, R5, R3 and R4.