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The Hox genes, being a subset of homeobox genes, arose more recently in evolution within the animal kingdom or Metazoa. Within the animal kingdom, Hox genes are present across the bilateria [10] (animals with a clear head-to-tail axis), and have also been found in Cnidaria such as sea anemones. [11]
Phylogenetic analysis of homeobox gene sequences and homeodomain protein structures suggests that the last common ancestor of plants, fungi, and animals had at least two homeobox genes. [21] Molecular evidence shows that some limited number of Hox genes have existed in the Cnidaria since before the earliest true Bilatera , making these genes ...
Hox genes determine where repeating parts, such as the many vertebrae of snakes, will grow in a developing embryo or larva. [9] Pax-6, already mentioned, is a classic toolkit gene. [48] Although other toolkit genes are involved in establishing the plant bodyplan, [49] homeobox genes are also found in plants, implying they are common to all ...
In plants, MADS-box genes are involved in controlling all major aspects of development, including male and female gametophyte development, embryo and seed development, as well as root, flower and fruit development. [12] [13] Some MADS-box genes of flowering plants have homeotic functions like the HOX genes of animals. [1]
Although plants have homeobox-containing genes, plant homeotic factors tend to possess MADS-box DNA binding domains. Animal genomes also possess a small number MADS-box factors. Thus, in the independent evolution of multicellularity in plants and animals, different eukaryotic transcription factor families were co-opted to serve homeotic functions.
Hox genes play a massive role in some amphibians and reptiles in their ability to regenerate lost limbs, especially HoxA and HoxD genes. [1]If the processes involved in forming new tissue can be reverse-engineered into humans, it may be possible to heal injuries of the spinal cord or brain, repair damaged organs and reduce scarring and fibrosis after surgery.
From the example above, if the descendant with genes A1 and B underwent another speciation event where gene A1 duplicated, the new species would have genes B, A1a, and A1b. In this example, genes A1a and A1b are symparalogs. [1] Vertebrate Hox genes are organized in sets of paralogs. Each Hox cluster (HoxA, HoxB, etc.) is on a different chromosome.
Among the most important of the toolkit genes are those of the Hox gene cluster, or complex. Hox genes, transcription factors containing the more broadly distributed homeobox protein-binding DNA motif, function in patterning the body axis. Thus, by combinatorially specifying the identity of particular body regions, Hox genes determine where ...