https://www.wikidoc.org/index.php?title=Clade&feed=atom&action=historyClade - Revision history2024-03-29T04:35:40ZRevision history for this page on the wikiMediaWiki 1.40.0https://www.wikidoc.org/index.php?title=Clade&diff=671438&oldid=prevWikiBot: Bot: Automated text replacement (-{{SIB}} + & -{{EH}} + & -{{EJ}} + & -{{Editor Help}} + & -{{Editor Join}} +)2012-08-08T23:55:29Z<p>Bot: Automated text replacement (-{{SIB}} + & -{{EH}} + & -{{EJ}} + & -{{Editor Help}} + & -{{Editor Join}} +)</p>
<p><b>New page</b></p><div><!--"assumptions about relationships about the description of" and other wording issues, the meaning of which I'm too uncertain about to fix myself; should be fixed by someone from a biology WikiProject who knows the terminology well. -SMcCandlish.--><br />
A '''clade''' is a [[taxonomy|taxonomic]] group of [[organism]]s comprising a single [[common ancestor]] and all the descendants of that ancestor. Any such group is considered to be a [[monophyletic]] group of organisms, and can be represented by both a [[phylogenetic]] analysis, as in a tree diagram, and by a [[cladogram]] (see [[cladistics]]), or simply as a taxonomic reference.<br />
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If a clade proves robust in different cladistic analyses using different sets of data, it may be adopted into taxonomy and become a [[taxon]]. Not all [[taxa]], however, are considered to be clades. [[Reptile]]s, for example, are a [[paraphyly|paraphyletic]] group because they do not include [[aves]] ([[birds]]), which are thought to also have evolved from the common ancestor of the reptiles. <br />
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In [[cladistics]], a clade that is located within another more inclusive clade is said to be "nested" within that clade. Nested clade analysis is beneficial in many ways. For instance, it enables the detection of range expansions in isolated geographic areas.<br />
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==Phylogenetic nomenclature== <br />
{{Original research|date=July 2007}}<!--Way too much opinion in here, bringing in fractal mathematics and other stuff that is off topic and unsupported with reference citations.--><br />
[[Phylogenetic nomenclature]] is formulated in terms of evolution and common descent rather than the [[type specimen]]s, categorical ranks, and [[morphology (biology)|morphological]] [[character (biology)|character]]s. The latter is used most commonly in cladistic analysis. Taxon names are strictly connected to [[phylogenetic tree]] topology and evolutionary history. In taxonomy, each name is attached to a clade taxonomic group containing a common ancestor and all its descendants. Phylogenetic nomenclature discards categorical ranks. The problem with ranks are evident when one considers biodiversity lineages and clades. Questions like "how many lineages are there?" or "how many clades are there?" become pointless, since there are no answers. These are relative concepts, illustrating the fractal nature of the tree of life and the need to let a phylogenetic hypothesis be the focus, rather than the categories, when biodiversity is quantified. Phylogenetic nomenclature helps to put focus on phylogenetic trees by offering an explicit link between names and parts of species history, that is, clades.<br />
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==Traditional binomial nomenclature==<br />
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In phylogenetics, [[Binomial nomenclature|binomial names]] are associated with the relationships of each described species. But this creates a problem because it makes assumptions about relationships about the description of the species identification. It suggests that species or genera are a unique category, and this contradicts the idea of recognizing only clades and lineages.<br />
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==Phylogenetic alternatives==<br />
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To avoid the pitfalls of traditional [[Linnaean taxonomy]] in phylogenetic nomenclature, three new methods of phylogenetic naming have been proposed: node-, stem-, and apomorphy-based. In node-based naming, taxon name A might refer to the least inclusive clade containing X and Y. In stem-based naming, A would refer to the most inclusive clade containing X and Y but not Z. In apomorphy (derived feature)-based naming, A would refer to the clade identified by a feature synapomorphic (sharing a derivation) with a feature in specimen (taxon) X. Differences between a traditional approach and these phylogenetic alternatives become obvious when the phylogenetic hypothesis changes. Comparison between the traditional Linnaean approach to nomenclature and a phylogenetic alternative (node-based naming). Suppose that all we want to do is to give a name ("A") to a clade containing X and Y. In the Linnaean system this means that we have to introduce names for sister taxa, assigning all taxa to the categories species, genus, and family, and designate type species. No explicit reference to phylogeny is made. The phylogenetic alternative provides an explicit reference to evolutionary history, and nothing but the clade containing X and Y needs to be named. When the hypothesis of relationship changes, the phylogenetic alternative is cleaner and more explicit about what it refers to. <br />
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{{phylo}}<br />
{{Evolution}}<br />
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==External links==<br />
* [http://scienceblogs.com/evolvingthoughts/2007/01/clade_1.php Evolving Thoughts: Clade]<br />
* [http://www.zo.utexas.edu/faculty/antisense/DownloadfilesToL.html DM Hillis, D Zwickl & R Gutell: ~3000 species Tree of Life] A cladogram?<br />
* [http://evolution.berkeley.edu/evolibrary/article/0_0_0/phylogenetics_01 Phylogenetic systematics, a.k.a. evolutionary trees] [[University of California, Berkeley]]<br />
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[[Category:Phylogenetics]]<br />
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