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Gene Switches

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Fruit fly

In the 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 development.


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