Apomorphy and synapomorphy

The word {{wikt-lang|en|synapomorphy}}—coined by German entomologist Willi Hennig—is derived from the Ancient Greek words {{wikt-lang|grc|σύν}} (sún), meaning "with, together"; {{wikt-lang|grc|ἀπό}} (apó), meaning "away from"; and {{wikt-lang|grc|μορφή}} (morphḗ), meaning "shape, form".

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Whether a character state is derived or ancestral is called character polarity. Since genealogical classifications are based on synapomorphies, there must be a way to determine which character state is derived and which is ancestral (or what is special and what is general, to use less evolutionarily freighted terminology) without reference to genealogical classifications, to avoid a circular argument. Some features have been recognized as unique to particular taxa for thousands of years (e.g., feathers for birds, or an internal bony skeleton for vertebrates), and these sorts of common-sense presence/absence characters provide a scaffold upon which the polarity of other characters can be inferred: feathered animals form a natural group; things that lack feathers are just the complement - everything else (mammals, sharks, plants, bacteria). Once a taxon called "birds" is recognized that is defined by the synapomorphy "presence of feathers", then the polarity of other characters present at greater or lesser levels of inclusiveness can be discovered and evaluated. This may identify larger clades, such as the diapsid skull that defines diapsids, or less inclusive clades, such as the syrinx that defines songbirds.

Lampreys and sharks share some features, like a nervous system, that are not synapomorphic because they are also shared by invertebrates. In contrast, the presence of jaws and paired appendages{{Cite web |last=andrewgillis |date=2016-04-19 |title=Gills, fins and the evolution of vertebrate paired appendages |url=https://thenode.biologists.com/gills-fins-evolution-vertebrate-paired-appendages/research/ |access-date=2024-06-09 |website=the Node |language=en}} in both sharks and dogs, but not in lampreys or close invertebrate relatives, identifies these traits as synapomorphies. This supports the hypothesis that dogs and sharks are more closely related to each other than to lampreys.

The concept of synapomorphy depends on a given clade in the tree of life. Cladograms are diagrams that depict evolutionary relationships within groups of taxa. These illustrations are accurate predictive device in modern genetics. They are usually depicted in either tree or ladder form. Synapomorphies then create evidence for historical relationships and their associated hierarchical structure. Evolutionarily, a synapomorphy is the marker for the most recent common ancestor of the monophyletic group consisting of a set of taxa in a cladogram.{{Cite journal |last=Novick |first=Laura R. |last2=Catley |first2=Kefyn M. |date=December 2007 |title=Understanding phylogenies in biology: the influence of a Gestalt Perceptual Principle |url=https://pubmed.ncbi.nlm.nih.gov/18194047 |journal=Journal of Experimental Psychology. Applied |volume=13 |issue=4 |pages=197–223 |doi=10.1037/1076-898X.13.4.197 |issn=1076-898X |pmid=18194047}} What counts as a synapomorphy for one clade may well be a primitive character or plesiomorphy at a less inclusive or nested clade. For example, the presence of mammary glands is a synapomorphy for mammals in relation to tetrapods but is a symplesiomorphy for mammals in relation to one another—rodents and primates, for example. So the concept can be understood as well in terms of "a character newer than" (autapomorphy) and "a character older than" (plesiomorphy) the apomorphy: mammary glands are evolutionarily newer than vertebral column, so mammary glands are an autapomorphy if vertebral column is an apomorphy, but if mammary glands are the apomorphy being considered then vertebral column is a plesiomorphy.

These phylogenetic terms are used to describe different patterns of ancestral and derived character or trait states as stated in the above diagram in association with apomorphies and synapomorphies.Roderick D.M. Page; Edward C. Holmes (14 July 2009). [https://books.google.com/books?id=p2lWhjuK8m8C Molecular Evolution: A Phylogenetic Approach]. John Wiley & Sons. {{ISBN|978-1-4443-1336-9}}.{{cite book | last1 = Calow | first1 = Peter P. | name-list-style = vanc |title=Encyclopedia of Ecology and Environmental Management |date=2009 |publisher=John Wiley & Sons |isbn=978-1-4443-1324-6 | oclc = 1039167559 | url = https://books.google.com/books?id=JKTeiqPBpM4C&pg=PA552 }}

• Symplesiomorphy – an ancestral trait shared by two or more taxa.
• Plesiomorphy – a symplesiomorphy discussed in reference to a more derived state.
• Pseudoplesiomorphy – a trait that cannot be identified as either a plesiomorphy or an apomorphy that is a reversal.{{cite book | first1 = David | last1 = Williams | first2 = Michael | last2 = Schmitt | first3 = Quentin | last3 = Wheeler | name-list-style = vanc | title = The Future of Phylogenetic Systematics: The Legacy of Willi Hennig | publisher = Cambridge University Press | date = July 2016 | url = https://books.google.com/books?id=J1GJDAAAQBAJ&pg=PA169 | isbn = 978-1-107-11764-8 }}
• Reversal – a loss of derived trait present in ancestor and the reestablishment of a plesiomorphic trait.
• Convergence – independent evolution of a similar trait in two or more taxa.
• Apomorphy – a derived trait. Apomorphy shared by two or more taxa and inherited from a common ancestor is synapomorphy. Apomorphy unique to a given taxon is autapomorphy.{{cite book | title = Plant Systematics | first = Michael G. | last = Simpson | name-list-style = vanc | location = Amsterdam | work = Elsevier | url = https://books.google.com/books?id=Ia2eIPVksMMC&pg=PA18 | date = 9 August 2011 | isbn = 9780080514048 }}{{cite book | first1 = Peter J. | last1 = Russell | first2 = Paul E. | last2 = Hertz | first3 = Beverly | last3 = McMillan | name-list-style = vanc | title = Biology: The Dynamic Science | url = https://books.google.com/books?id=dVIWAAAAQBAJ&pg=PT572 | isbn = 978-1-285-41534-5 | publisher = Cengage Learning | year = 2013 }}{{cite web | title = Basics of Cladistic Analysis | first = Diana | last = Lipscomb | name-list-style = vanc | publisher = George Washington University | location = Washington D.C. | year = 1998| url = https://www2.gwu.edu/~clade/faculty/lipscomb/Cladistics.pdf }}{{cite book | first = Supratim | last = Choudhuri | name-list-style = vanc | title = Bioinformatics for Beginners: Genes, Genomes, Molecular Evolution, Databases and Analytical Tools | edition = 1st | publisher = Academic Press |isbn=978-0-12-410471-6 | oclc = 950546876 | url = https://books.google.com/books?id=Guj1AgAAQBAJ&pg=PA51 | page = 51 | date = 2014-05-09 }}
• Synapomorphy/homology – a derived trait that is found in some or all terminal groups of a clade, and inherited from a common ancestor, for which it was an autapomorphy (i.e., not present in its immediate ancestor).
• Underlying synapomorphy – a synapomorphy that has been lost again in many members of the clade. If lost in all but one, it can be hard to distinguish from an autapomorphy.
• Autapomorphy – a distinctive derived trait that is unique to a given taxon or group.Appel, Ron D.; Feytmans, Ernest. Bioinformatics: a Swiss Perspective."Chapter 3: Introduction of Phylogenetics and its Molecular Aspects." World Scientific Publishing Company, 1st edition. 2009.
• Homoplasy in biological systematics is when a trait has been gained or lost independently in separate lineages during evolution. This convergent evolution leads to species independently sharing a trait that is different from the trait inferred to have been present in their common ancestor.{{cite web | title = Similarity Happens! The Problem of Homoplasy | url = https://evolutionnews.org/2012/04/similarity_happ/ | first = Ann | last = Gauger | name-list-style = vanc | date = April 17, 2012 | work = Evolution Today & Science News }}{{cite book | first1 = Michael J. | last1 = Sanderson | first2 = Larry | last2 = Hufford | name-list-style = vanc | title = Homoplasy: The Recurrence of Similarity in Evolution | publisher = Elsevier | date = 21 October 1996 | url = https://books.google.com/books?id=WWGNzeNmRUYC&pg=PA92 | isbn = 978-0-08-053411-4 | oclc = 173520205 }}{{cite journal | vauthors = Brandley MC, Warren DL, Leaché AD, McGuire JA | title = Homoplasy and clade support | journal = Systematic Biology | volume = 58 | issue = 2 | pages = 184–98 | date = April 2009 | pmid = 20525577 | doi = 10.1093/sysbio/syp019 | doi-access = free }}
• Parallel homoplasy – derived trait present in two groups or species without a common ancestor due to convergent evolution.{{cite journal | first = James W. | last = Archie | name-list-style = vanc | title = Homoplasy Excess Ratios: New Indices for Measuring Levels of Homoplasy in Phylogenetic Systematics and a Critique of the Consistency Index | journal = Systematic Biology | volume = 38 | issue = 1 | date = September 1989 | pages = 253–269 | doi = 10.2307/2992286 | jstor = 2992286 }}
• Reverse homoplasy – trait present in an ancestor but not in direct descendants that reappears in later descendants.{{cite journal | vauthors = Wake DB, Wake MH, Specht CD | title = Homoplasy: from detecting pattern to determining process and mechanism of evolution | journal = Science | volume = 331 | issue = 6020 | pages = 1032–5 | date = February 2011 | pmid = 21350170 | doi = 10.1126/science.1188545 | bibcode = 2011Sci...331.1032W | s2cid = 26845473}}
• {{cite press release |date=February 25, 2011 |title=Homoplasy: A good thread to pull to understand the evolutionary ball of yarn |website=ScienceDaily |url=https://www.sciencedaily.com/releases/2011/02/110224161512.htm}}
• Hemiplasy is the case where a character that appears homoplastic given the species tree actually has a single origin on the associated gene tree.{{cite journal | vauthors = Avise JC, Robinson TJ | title = Hemiplasy: a new term in the lexicon of phylogenetics | journal = Systematic Biology | volume = 57 | issue = 3 | pages = 503–7 | date = June 2008 | pmid = 18570042 | doi = 10.1080/10635150802164587 | doi-access = free }}{{cite journal | vauthors = Copetti D, Búrquez A, Bustamante E, Charboneau JL, Childs KL, Eguiarte LE, Lee S, Liu TL, McMahon MM, Whiteman NK, Wing RA, Wojciechowski MF, Sanderson MJ | title = Extensive gene tree discordance and hemiplasy shaped the genomes of North American columnar cacti | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 114 | issue = 45 | pages = 12003–12008 | date = November 2017 | pmid = 29078296 | pmc = 5692538 | doi = 10.1073/pnas.1706367114 | bibcode = 2017PNAS..11412003C | doi-access = free }} Hemiplasy reflects gene tree-species tree discordance due to the multispecies coalescent.

{{reflist}}

• [http://www.ucmp.berkeley.edu/IB181/VPL/Phylo/Phylo2.html Cladistics], Berkeley

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Category:Phylogenetics

Category:Evolutionary biology terminology

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