交流英语Concepts of monopoly, polyphyly, & paraphyly
A taxon (pl. taxa) is any group of organisms that is given a formal taxonomic name. Looly, a monophyletic taxon is one that includes a group of organisms descended from a single ancestor , whereas a polyphyletic taxon is compod of unrelated organisms descended from more than one ancestor.
labourer>作家用英语怎么说The loo definitions fail to recognize the fact that all organisms are related, therefore any conceivable group is logically "monophyletic". In modern usage, a monophyletic taxon is defined as one that includes the most recent common ancestor of a group of organisms, and all of its descendents
[as in (a)]. Such groups are sometimes called holophyletic. It is also possible to recognize a paraphyletic taxon as one that includes the most recent common ancestor, but not all of its descendents [as in (c)]. A polyphyletic taxon is defined as one that does not include the common ancestor of all members of the taxon [as in (b)].
Well-known monophyletic taxa include Mammalia and Aves (modern birds), recognizable as all furry and feathered vertebrates, respectively. Paraphyletic taxa include Pisces and Reptilia, the former comprising all ray-finned fish but excluding terrestrial descendants of fleshy-finned fish, and the latter comprising all scaly tetrapods but excluding mammals and birds with their modified scales. Polyphyletic taxa once in common usage include Agnatha for jawless lampreys and hagfish, and Inctivora for various toothless, inct-eating mammals such as anteaters and armadillos. Note that the latter groups are defined by 'abnce' characters, and that although redwood trees are jawless and toothless, they are not included in tho taxa.
Taxonomists tend to fall into two schools, "Evolutionary" or "traditional" systematics versus "Phylogenetic" or "cladistic" systematics. Since the 1970s, "phylogenetic systematics" has been replacing "traditional systematics" Becau the older literature and textbooks often u "evolutionary" classifications, the student must understand both systems.
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An unfortunate circumstance for the student is that the two schools u the same terms, but in different ways, and often refu to recognize the alternative usage. Evolutionary taxonomists claim to recognize only "monophyletic" taxa, but u the term to include both holophyletic and paraphyletic taxa. Phylogenetic taxonomists also claim to recognize only "monophyletic" taxa, but limit the term to what is defined above as "holophyletic," although most reject that particular term. Both schools reject the u of polyphyletic taxa, although most phylogenetic taxonomists would u that term to included paraphyletic taxa.
Homework: The diagram above recognizes Taxa 1, 2, & 3 as examples of "monophyletic", "polyphyletic", and "paraphyletic" groups, respectively. (1) In the diagram, identify two additional examples each of groups that would be considered
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"holophyletic," "polyphyletic," and "paraphyletic". (2) Identify all possible "holophyletic" taxa.糖醋藕片的做法>萨特名言
Figure © 1999 by Addison Wesley Longman; Text material © 2012 by Steven M. Carr
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