GENETIC-ANALYSIS OF THE ADDITIONAL SEX COMBS LOCUS OF DROSOPHILA-MELANOGASTER

Additional sex combs (Asx) is a member of the Polycomb group of genes, which are thought to be required for maintenance of chromatin structu re. To better understand the function of Asx, we have isolated nine ne w alleles, each of which acts like a gain of function mutation. Asx is required for normal determination of segment identity. Asx(P1) shows an unusual phenotype in that anterior and posterior homeotic transform ations are seen in the same individuals, suggesting that Asx(P1) might upset chromatin structure in a way that makes both activation and rep ression of homeotic genes more difficult. Analysis of embryonic and ad ult phenotypes of Asx alleles suggests that Asx is required zygoticall y for determination of segment number and polarity. The expression pat tern of even-skipped is altered in Asx mutant embryos, suggesting that Asx is required for normal expression of this gene. We have transposo n-tagged the Asx gene, and can thus begin molecular analysis of its fu nction.