Genetic analysis of enhancer of split, a locus involved in neurogenesis in Drosophila melanogaster.

Enhancer of split (E(spl)), one of the neurogenic loci of Drosophila, is uncovered by the deletion Df(3R)E(spl)(R-B251) with breakpoints at 96F8 and 96F13. We describe here the results of a genetic analysis of this chromosomal interval. Thirty-one mutations in genes of this region were recovered during various programs of mutagenesis. In addition, we included the spontaneous mutations E(spl)(D) and groucho (gro), which are known to map to this region, in our study. These 33 mutations define four lethal complementation groups, one of which includes E(spl)(D) and gro. Mutations of the E(spl) group behave as complementing and noncomplementing pseudoalleles, defining different functions. Alleles are classified according to their complementation behavior in two different ways: with respect to their viability as heterozygotes with other lethal alleles and with respect to gro and to E(spl)(D). The phenotypes of these mutations and the pattern of heteroallelic complementation speak in favor of a considerable genetic complexity of the E(spl) locus.