UBX Background Information In Drosophila melanogaster, segment identity is determined by specific expression of homeotic genes (Hox) (1). The Hox expression pattern is first initiated by gap and pair-rule genes and then maintained by genes of the Polycomb-group (Pc-G) and the trithorax-group (trx-G) (1). Ultrabithorax (Ubx), a homeodomain containing trascription factor, is essential for the proper patterning of the posterior thorax and anterior abdomen in Drosophila (2,3). Ubx is the sole Hox gene responsible for the differential development of the forewing and haltere in Drosophila (4). Mutations in Ubx result in the transformation of the third thoracic (the haltere and third leg ) segment into the second thoracic (wing and second leg) segment (5).
