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Toolkit: replaced an instance of the word "toolbox" with "toolkit" to maintain consistency across the entire page

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[[File:Hoxgenesoffruitfly.svg|Expression of all 8 [[Hox gene]]s in the fruit fly ''[[Drosophila melanogaster]]''|thumb|right|400px]]

The '''evo-devo gene toolkit''' is the small subset of [[gene]]s in an organism's [[genome]] whose products control the organism's [[developmental biology|embryonic development]]. '''Toolkit genes''' are central to the synthesis of [[molecular genetics]], [[palaeontology]], [[evolution]] and developmental biology in the science of [[evolutionary developmental biology]] (evo-devo). Many of them are ancient and highly [[conserved sequence|conserved]] among animal [[Phylum|phyla]].

==Toolkit==

Toolkit genes are highly [[conserved sequence|conserved]] among [[Phylum|phyla]], meaning that they are ancient, dating back to the [[Urbilaterian|last common ancestor of bilaterian animals]]. For example, that ancestor had at least 7 [[Pax genes]] for [[transcription factor]]s.<ref>{{cite journal |last1=Friedrich |first1=Markus |title=Evo-Devo gene toolkit update: at least seven Pax transcription factor subfamilies in the last common ancestor of bilaterian animals Authors|journal=Evolution & Development |date=2015 |volume=17 |issue=5 |pages=255–257 |doi=10.1111/ede.12137 |pmid=26372059|s2cid=5414439 |url=https://zenodo.org/record/1233833 }}</ref>

Differences in deployment of toolkit genes affect the body plan and the number, identity, and pattern of body parts. The majority of toolkit genes are components of signaling pathways and encode for the production of transcription factors, [[cell adhesion]] proteins, cell surface [[receptor (biochemistry)|receptor]] proteins (and signalling [[Ligand (biochemistry)|ligands]] that bind to them), and secreted [[morphogens]]; all of these participate in defining the fate of undifferentiated cells, generating spatial and temporal patterns that, in turn, form the [[body plan]] of the organism. 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 [[Limb (anatomy)|limbs]] and other [[Anatomy|body]] segments will grow in a developing [[embryo]] or [[larva]]. A [[wikt:paradigm|paradigm]]atic toolkit gene is ''[[Pax6]]/eyeless'', which controls [[eye]] formation in all animals. It has been found to produce eyes in mice and ''[[Drosophila]]'', even if mouse ''Pax6/eyeless'' was expressed in ''Drosophila''.<ref>{{cite journal |author1=Xu, P. X. |author2=Woo, I. |author3=Her, H. |author4=Beier, D. R. |author5=Maas, R. L. |year=1997 |title=Mouse Eya homologues of the Drosophila eyes absent gene require Pax6 for expression in lens and nasal placode |journal=Development |volume=124 |issue=1 |pmid=9006082 |pages=219–231 |doi=10.1242/dev.124.1.219 }}</ref>

This means that a big part of the morphological evolution undergone by organisms is a product of variation in the genetic toolkit, either by the genes changing their expression pattern or acquiring new functions. A good example of the first is the enlargement of the beak in Darwin's large ground-finch ([[large ground-finch|''Geospiza magnirostris'']]), in which the gene ''[[Bone morphogenetic protein|BMP]]'' is responsible for the larger beak of this bird, relative to the other finches.<ref>{{cite journal |author1=Abzhanov, A. |author2=Protas, M. |author3=Grant, B. R. |author4=Grant, P. R. |author5=Tabin, C. J. |s2cid=17226774 |year=2004 |title=Bmp4 and Morphological Variation of Beaks in Darwin's Finches |journal=Science |volume=305 |issue=5689| doi=10.1126/science.1098095 |pages=1462–1465 |pmid=15353802 |bibcode=2004Sci...305.1462A}}</ref>

The loss of legs in [[snake]]s and other [[Squamata|squamates]] is another good example of genes changing their expression pattern. In this case the gene ''[[Dlx (gene)|Distal-less]]'' is very under-expressed, or not expressed at all, in the regions where limbs would form in other [[tetrapod]]s.<ref>{{cite journal |author1=Cohn, M. J. |author2=Tickle, C. |title=Developmental basis of limblessness and axial patterning in snakes |year=1999 |journal=Nature |volume=399 |pages=474–479 |pmid=10365960 |issue=6735 |doi=10.1038/20944 |bibcode=1999Natur.399..474C|s2cid=4309833 }}</ref>
In 1994, [[Sean B. Carroll]]'s team made the groundbreaking discovery that this same gene determines the [[eyespot (mimicry)|eyespot pattern]] in [[butterfly]] [[wing]]s, showing that toolkit genes can change their function.<ref>{{cite journal |author1=Beldade, P. |author2=Brakefield, P. M. |author3=Long, A.D. |year=2002 |title=Contribution of Distal-less to quantitative variation in butterfly eyespots |journal=Nature |volume=415 |issue=6869 |pages=315–318 |pmid=11797007 |doi=10.1038/415315a|s2cid=4430563 }}</ref><ref>{{cite journal |last1=Werner |first1=Thomas|title=Leopard Spots and Zebra Stripes on Fruit Fly Wings|journal=Nature Education |date=2015 |volume=8 |issue=2 |page=3 |url=https://www.nature.com/scitable/topicpage/leopard-spots-and-zebra-stripes-on-fruit-131087142}}</ref><ref>{{cite journal |last1=Carroll |first1=Sean B. |author-link=Sean B. Carroll |display-authors=etal |title=Pattern formation and eyespot determination in butterfly wings |journal=Science |date=1994 |volume=265 |issue=5168 |pages=109–114|doi=10.1126/science.7912449 |pmid=7912449 |bibcode=1994Sci...265..109C }}</ref>

Toolkit genes, as well as being highly conserved, also tend to evolve the same function [[Convergent evolution|convergently]] or [[Parallel Evolution|in parallel]]. Classic examples of this are the already mentioned ''Distal-less'' gene, which is responsible for appendage formation in both tetrapods and insects, or, at a finer scale, the generation of wing patterns in the butterflies ''[[Heliconius erato]]'' and ''[[Heliconius melpomene]]''. These butterflies are [[Müllerian mimicry|Müllerian mimics]] whose coloration pattern arose in different evolutionary events, but is controlled by the same genes.<ref>{{cite journal |author1=Baxter, S. W. |author2=Papa, R. |author3=Chamberlain, N. |author4=Humphray, S. J. |author5=Joron, M. |author6=Morrison, C. |author7=ffrench-Constant, R. H. |author8=McMillan, W. O. |author9=Jiggins, C. D. |year=2008 |title=Convergent Evolution in the Genetic Basis of Mullerian Mimicry in Heliconius Butterflies |journal=Genetics |volume=180 |issue=3 |pages=1567–1577 | pmid=18791259 |pmc=2581958 | doi=10.1534/genetics.107.082982}}</ref>
This supports [[Marc Kirschner]] and [[John C. Gerhart]]'s theory of [[Facilitated variation|Facilitated Variation]], which states that morphological evolutionary novelty is generated by regulatory changes in various members of a large set of conserved mechanisms of development and physiology.<ref>{{cite journal | last1=Gerhart |first1=John |last2=Kirschner |first2=Marc |year=2007 |title=The theory of facilitated variation |journal=Proceedings of the National Academy of Sciences | pmid=17494755 |volume=104 | pmc=1876433 |issue=suppl1 |doi=10.1073/pnas.0701035104 |pages=8582–8589|bibcode=2007PNAS..104.8582G|doi-access=free }}</ref>

==See also==

* ''[[Endless Forms Most Beautiful (book)|Endless Forms Most Beautiful]]''
* ''[[How the Snake Lost its Legs]]''

==References==

{{reflist|30em}}

[[Category:Evolutionary biology]]
[[Category:Animal developmental biology]]
[[Category:Genetics]]
[[Category:Evolutionary developmental biology]]

Evo-devo gene toolkit - История изменений

Admin: 1 версия импортирована

ru>Lazilexi: /* Toolkit */ replaced an instance of the word "toolbox" with "toolkit" to maintain consistency across the entire page