Bithorax complex

[5] The first homeotic mutation to be isolated was the bithorax (bx) mutant in 1915 by Calvin Bridges,[6] which was later worked on and better characterized as a gene cluster by Edward B.

[5] Lewis found that BX-C contained genes that code for proteins controlling the levels of thoracic and abdominal development, and postulated that at least four of these genes were regulated by cis-regulatory elements, as well as a separate locus (Polycomb) that acted as a repressor.

[5] However, subsequent research has found that the complex only contains three genes that are differentially expressed in each parasegment.

[10] During embryonic development, regulation of BX-C expression occurs on the level of units called parasegments.

[10] The parasegment-specific expression patterns of the BX-C genes are controlled by large and complex cis-regulatory regions.