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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.
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 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 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.
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.
In evolutionary developmental biology, homeosis is the transformation of one organ into another, arising from mutation in or misexpression of certain developmentally critical genes, specifically homeotic genes. In animals, these developmental genes specifically control the development of organs on their anteroposterior axis. [1]
Within the metazoa, homeotic genes control differentiation along major body axes, and pax genes (especially PAX6) help to control the development of the eye and other sensory organs. The deep homology applies across widely separated groups, such as in the eyes of mammals and the structurally quite different compound eyes of insects. [3]
The homeotic genes are activated by gap genes and pair-rule genes. The Antennapedia complex and the bithorax complex on the third chromosome contain the major homeotic genes required for specifying segmental identity (actually parasegmental identity). These genes are transcription factors and are expressed in overlapping regions that correlate ...