Mosaic animals in which the retina is homozygous for svpsd-27 (generated using the "EGUF/hid" system) have normal external eye morphology but show defects in a phototaxis assay. The electroretinogram of mosaic animals in which the retina is homozygous for svpsd-27 has defective on/off transients. Hemizygotes and homozygotes die as embryos.