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Homeotic genes are genes which regulate the development of anatomical structures in various organisms such as echinoderms, [1] insects, mammals, and plants. Homeotic genes often encode transcription factor proteins, and these proteins affect development by regulating downstream gene networks involved in body patterning.
The homeotic selector genes were discovered through the genetic analysis of Drosophila over 80 years ago [citation needed].Unusual disturbances were found in the organization of the adult fly, resulting in misplaced limbs, such as legs developing where antennae usually develop or an extra pair of wings developing where halteres should be.
The homeobox gene clusters studied by Ed Lewis were named the Hox genes, although many more homeobox genes are encoded by animal genomes than those in the Hox gene clusters. The homeotic-function of certain proteins was first postulated to be that of a "selector" as proposed by Antonio Garcia-Bellido. [11]
Mutations in these homeotic genes cause displacement of body segments during embryonic development. This is called ectopia. For example, when one gene is lost the segment develops into a more anterior one, while a mutation that leads to a gain of function causes a segment to develop into a more posterior one.
The B and C genes establish the identity of the stamens and the carpels only require C genes to be active. Type A and C genes are reciprocally antagonistic. [10] The fact that these homeotic genes determine an organ's identity becomes evident when a gene that represents a particular function, for example the A gene, is not expressed.
The Hox genes are named for the homeotic phenotypes that result when their function is disrupted, wherein one segment develops with the identity of another (e.g. legs where antennae should be). Hox genes in different phyla have been given different names, which has led to confusion about nomenclature.
Agamous (AG) is a homeotic gene and MADS-box transcription factor from Arabidopsis thaliana.The TAIR AGI number is AT4G18960.. The identity of a floral organ is determined by particular combinations of homeotic genes, these genes derive from a group of undifferentiated cells known as the floral meristem.
The gene complex is located on the right arm of chromosome 3 alongside the other homeotic gene complex, the Antennapedia (Antp) complex. [1] It is over 300 kb long and contains nine distinct cis-regulatory domains. [2] The three transcription units, Ubx, abd-A, and Abd-B, are spread out evenly on the complex. [6]