fly seen here, a genetic mutation caused the Ubx gene to be turned off, during the larval stage, in the
third thoracic segment. This is the segment that normally produces the haltere.
Notice anything different? Instead of a pair of halteres, the fly has a second
set of wings. With the switch of that single Hox gene, Ubx, from on
to off, the third thoracic segment became an additional second thoracic segment
and the pair of halteres became a second pair of wings. This illustrates the
remarkable ability of transcription factors like Ubx to control patterning as well as cell type during