Wustmann, G., Szidonya, J., Taubert, H., Reuter, G. (1989). The genetics of position-effect variegation modifying loci in Drosophila melanogaster. Molec. gen. Genet. 217: 520--527.
The dose dependent effects of position-effect variegation (PEV) modifying genes were studied in chromosome arms 2L, 2R and
3R. Four groups of PEV modifying genes can be distinguished: haplo-abnormal suppressor and enhancer loci with or without a
triplo-effect. Using duplications four triplo-abnormal suppressor and four triplo-abnormal enhancer functions were localized.
In two cases we proved that these functions correspond to a converse haplo-abnormal one. Altogether 43 modifier loci were
identified. Most of these loci proved not to display significant triplo-effects (35). The group of haplo-abnormal loci with
a triplo-effect may represent genes which play an important role in heterochromatin packaging.
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