Phenogenetics of a suppressor and an enhancer gene of the lozenge34k allel of Drosophila melanogaster.

The recessive sex-linked gene, lozenge34k, was initially identified on the basis of its effect on the compound eye of Drosophila melanogaster. However, its pleiotropic effects include modification of the antennae, legs and female reproductive structures as well. Two modifier genes, a third chromosome suppressor, su(lz34k), and a fourth chromosome enhancer, spae(lz), have been previously described and their effects on the various mutant characters of the lozenge34k phenotype were the basis of this study. These investigations included scanning electron microscope observations of the external morphology of the compound eye, a quantitative determination of the effects of the mutant genes on the tarsal claws, antennae and female reproductive capacity, and an examination of the functional ability of the compound eye. It was found that the modifier genes had little effect on the aspects of the lozenge34k phenotype other than the compound eye. The enhancer seems to suppress the lozenge phenotype with regard to the length of the antenna but otherwise there is no effect of the modifiers with regard to antennae, tarsal claws, spermathecae or female reproductive capacity (the number of eggs oviposited or the number of adult progeny ensuring from females tested). The lozenge-enhanced males also differed significantly from the other types in being less successful at inseminating females in the light. The lozenge and lozenge-suppressed males were more successful than the lozenge-enhanced but less so than the wild type. This can be related to their ability to "see" since in the dark all types were at an equal disadvantage. Wild flies exhibited a positive phototactic response, lozenge were significantly less responsive, and both the suppressed and enhanced flies were even less so. Compound-X females lacking the lozenge34k allele were tested for phototaxis. Those homozygous for the suppressor were significantly less phototactic than the others indicating that the suppressor alone has a phenotype at this level. Except for the phototactic response of lozenge-suppressed flies, the functional ability of the compound eye can be correlated with its morphology.