GENETIC-ANALYSIS OF THE LOZENGE GENE-COMPLEX IN DROSOPHILA-MELANOGASTER - ADULT VISUAL-SYSTEM PHENOTYPES

Mutations at the lozenge (lz) locus are pleiotropic, primarily affecti ng the sense organs for sight, smell and taste. To better understand t he role that lz plays in the visual system, we investigated its comple x genetics and the effect mutations have on the structure of the compo und eye. Complementation analysis within the it locus reveals two func tional units necessary for a normal eye, cistrons A and B. Previous re combination studies identified four subloci spanning 0.14 m.u. Cistron A mutations map to the distal-most spectacle sub-locus, which has bee n identified as an insertion point for P-elements. Southern blotting a nd chromosomal in situ hybridization show that P-allele lz(mr2) contai ns a single P-element; a cosmid clone derived from lz(mr2) confirms th at the P-element is defective. Mutants of both cistrons perturb lens s tructure and eye pigmentation. However, the extent of the defects diff ers between the most severe mutations of the two cistrons. Within the eye, failure to form the fenestrated membrane permits photoreceptor ne urons to ''fall'' into the brain disrupting neural structure. Our anal ysis shows that It exerts control over the identity of cone cells, pig ment cells and photoreceptor neurons.