View source for Polyploidy

{{Short description|Condition where cells have more than two sets of chromosomes}}
{{Distinguish|text="polypoid", resembling a [[polyp (zoology)|polyp]]}}
[[File:Haploid, diploid ,triploid and tetraploid.svg|thumb|This image shows haploid (single), diploid (double), triploid (triple), and tetraploid (quadruple) sets of chromosomes. Triploid and tetraploid chromosomes are examples of polyploidy.]]

'''Polyploidy''' is a condition in which the [[biological cell|cell]]s of an [[organism]] have more than two paired sets of ([[Homologous chromosome|homologous]]) [[chromosome]]s. Most species whose cells have [[Cell nucleus|nuclei]] ([[eukaryotes]]) are [[diploid]], meaning they have two complete sets of chromosomes, one from each of two parents; each set contains the same number of chromosomes, and the chromosomes are joined in pairs of homologous chromosomes. However, some organisms are '''polyploid'''. Polyploidy is especially common in plants. Most eukaryotes have diploid [[somatic cells]], but produce [[haploid]] [[gametes]] (eggs and sperm) by [[meiosis]]. A [[Ploidy|monoploid]] has only one set of chromosomes, and the term is usually only applied to cells or organisms that are normally diploid. Males of [[bee]]s and other [[Hymenoptera]], for example, are monoploid. Unlike animals, [[plants]] and multicellular [[algae]] have [[Biological life cycle|life cycle]]s with two [[alternation of generations|alternating multicellular generations]]. The [[gametophyte]] generation is haploid, and produces gametes by [[mitosis]]; the [[sporophyte]] generation is diploid and produces [[spores]] by [[meiosis]].

Polyploidy is the result of whole-genome duplication during the evolution of species. It may occur due to abnormal [[cell division]], either during mitosis, or more commonly from the failure of chromosomes to separate during meiosis or from the fertilization of an egg by more than one sperm.<ref>{{Cite book| vauthors = Solomon E |title=Solomon/Martin/Martin/Berg, Biology|publisher=Cengage Learning|year=2014|isbn=978-1-285-42358-6|page=344}}</ref> In addition, it can be induced in plants and [[cell culture]]s by some chemicals: the best known is [[colchicine]], which can result in chromosome doubling, though its use may have other less obvious consequences as well. [[Oryzalin]] will also double the existing chromosome content.

Among [[mammal]]s, a high frequency of polyploid cells is found in organs such as the brain, liver, heart, and bone marrow.<ref>{{cite journal | vauthors = Zhang S, Lin YH, Tarlow B, Zhu H | title = The origins and functions of hepatic polyploidy | journal = Cell Cycle | volume = 18 | issue = 12 | pages = 1302–1315 | date = June 2019 | pmid = 31096847 | pmc = 6592246 | doi = 10.1080/15384101.2019.1618123 }}</ref> It also occurs in the somatic cells of other [[animal]]s, such as [[goldfish]],<ref>{{cite journal |doi=10.1007/BF00293307 |title=Diploid-tetraploid relationship among old-world members of the fish family Cyprinidae |year=1967 | vauthors = Ohno S, Muramoto J, Christian L, Atkin NB |journal=Chromosoma |volume=23 |issue=1 |pages=1–9 }}</ref> [[salmon]], and [[salamander]]s. It is common among [[fern]]s and flowering [[plant]]s (see ''[[Hibiscus rosa-sinensis]]''), including both wild and cultivated [[species]]. [[Wheat]], for example, after millennia of [[Hybrid (biology)|hybridization]] and modification by humans, has strains that are '''diploid''' (two sets of chromosomes), '''tetraploid''' (four sets of chromosomes) with the common name of [[durum]] or macaroni wheat, and '''hexaploid''' (six sets of chromosomes) with the common name of bread wheat. Many agriculturally important plants of the genus ''[[Brassica]]'' are also tetraploids. [[Sugarcane]] can have ploidy levels higher than '''octaploid'''.<ref>
:{{cite journal | vauthors = Manimekalai R, Suresh G, Govinda Kurup H, Athiappan S, Kandalam M | title = Role of NGS and SNP genotyping methods in sugarcane improvement programs | journal = Critical Reviews in Biotechnology | volume = 40 | issue = 6 | pages = 865–880 | date = September 2020 | pmid = 32508157 | doi = 10.1080/07388551.2020.1765730 }}
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:This review cites this study:
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:{{cite journal | vauthors = Vilela MM, Del Bem LE, Van Sluys MA, de Setta N, Kitajima JP, Cruz GM, Sforça DA, de Souza AP, Ferreira PC, Grativol C, Cardoso-Silva CB, Vicentini R, Vincentz M | display-authors = 6 | title = Analysis of Three Sugarcane Homo/Homeologous Regions Suggests Independent Polyploidization Events of Saccharum officinarum and Saccharum spontaneum | journal = Genome Biology and Evolution | volume = 9 | issue = 2 | pages = 266–278 | date = February 2017 | pmid = 28082603 | pmc = 5381655 | doi = 10.1093/gbe/evw293 }}
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Polyploidization can be a mechanism of&nbsp;[[sympatric speciation]]&nbsp;because polyploids are usually unable to interbreed with their diploid ancestors. An example is the plant ''[[Erythranthe peregrina]]''. Sequencing confirmed that this species originated from ''E. × robertsii'', a sterile triploid hybrid between ''E. guttata'' and ''E. lutea,'' both of which have been introduced and naturalised in the United Kingdom. New populations of ''E. peregrina'' arose on [[Scotland|the Scottish mainland]] and the [[Orkney Islands]] via genome duplication from local populations of ''E. × robertsii''.<ref>{{cite journal | vauthors = Vallejo-Marín M, Buggs RJ, Cooley AM, Puzey JR | title = Speciation by genome duplication: Repeated origins and genomic composition of the recently formed allopolyploid species Mimulus peregrinus | journal = Evolution; International Journal of Organic Evolution | volume = 69 | issue = 6 | pages = 1487–1500 | date = June 2015 | pmid = 25929999 | pmc = 5033005 | doi = 10.1111/evo.12678 }}</ref> Because of a rare genetic mutation, ''E. peregrina'' is not sterile.<ref name="Fessenden">{{cite magazine| vauthors = Fessenden M |title=Make Room for a New Bloom: New Flower Discovered|url=https://www.scientificamerican.com/gallery/make-room-for-a-new-bloom-new-flower-discovered/|magazine=Scientific American|access-date=22 February 2017}}</ref> 

On the other hand, polyploidization can also be a mechanism for a kind of 'reverse speciation',<ref name="auto">{{Cite journal |last1=Schmickl |first1=Roswitha |last2=Yant |first2=Levi |date=April 2021 |title=Adaptive introgression: how polyploidy reshapes gene flow landscapes |url=|journal=New Phytologist |language=en |volume=230 |issue=2 |pages=457–461 |doi=10.1111/nph.17204 |pmid=33454987 |bibcode=2021NewPh.230..457S |issn=0028-646X|doi-access=free }}</ref> whereby gene flow is enabled following the polyploidy event, even between lineages that previously experienced no gene flow as diploids. This has been detailed at the genomic level in ''Arabidopsis arenosa'' and ''Arabidopsis lyrata''.<ref name="auto1">{{Cite journal |last1=Marburger |first1=Sarah |last2=Monnahan |first2=Patrick |last3=Seear |first3=Paul J. |last4=Martin |first4=Simon H. |last5=Koch |first5=Jordan |last6=Paajanen |first6=Pirita |last7=Bohutínská |first7=Magdalena |last8=Higgins |first8=James D. |last9=Schmickl |first9=Roswitha |last10=Yant |first10=Levi |date=2019-11-18 |title=Interspecific introgression mediates adaptation to whole genome duplication |journal=Nature Communications |language=en |volume=10 |issue=1 |page=5218 |doi=10.1038/s41467-019-13159-5 |issn=2041-1723 |pmc=6861236 |pmid=31740675|bibcode=2019NatCo..10.5218M }}</ref> Each of these species experienced independent autopolyploidy events (within-species polyploidy, described below), which then enabled subsequent interspecies gene flow of adaptive alleles, in this case stabilising each young polyploid lineage.<ref>{{Cite journal |last1=Seear |first1=Paul J. |last2=France |first2=Martin G. |last3=Gregory |first3=Catherine L. |last4=Heavens |first4=Darren |last5=Schmickl |first5=Roswitha |last6=Yant |first6=Levi |last7=Higgins |first7=James D. |date=2020-07-15 |title=A novel allele of ASY3 is associated with greater meiotic stability in autotetraploid Arabidopsis lyrata |journal=PLOS Genetics |language=en |volume=16 |issue=7 |article-number=e1008900 |doi=10.1371/journal.pgen.1008900 |doi-access=free |issn=1553-7404 |pmc=7392332 |pmid=32667955}}</ref> Such polyploidy-enabled adaptive introgression may allow polyploids at act as 'allelic sponges', whereby they accumulate cryptic genomic variation that may be recruited upon encountering later environmental challenges.<ref name="auto"/>

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== Terminology ==

=== Types ===
{{Redirect|Triploid|the human chromosomal disorder (69 XXX, etc.)|Triploid syndrome}}
{{anchor|Polyploid types}}
[[File:Organ-specific patterns of endopolyploidy in the giant ant Dinoponera australis - JHR-037-113-g001.jpg|thumb|upright=1.25|Organ-specific patterns of endopolyploidy (from 2''x'' to 64''x'') in the giant ant ''[[Dinoponera australis]]'']]'''Polyploid''' types are labeled according to the number of chromosome sets in the [[cell nucleus|nucleus]]. The letter ''x'' is used to represent the number of chromosomes in a single set:

*'''haploid''' (one set; 1''x''), for example male [[Myrmica rubra|European fire ant]]s
*'''diploid''' (two sets; 2''x''), for example [[human]]s
*'''triploid''' (three sets; 3''x''<!-- Sic, not "×"-->), for example sterile [[Crocus sativus|saffron crocus]], or [[parthenocarpy|seedless watermelons]], also common in the [[phylum]] [[Tardigrada]]<ref>{{cite journal| vauthors = Bertolani R |year=2001|title=Evolution of the reproductive mechanisms in Tardigrades: a review|journal=Zoologischer Anzeiger|volume=240|issue=3–4|pages=247–252|doi=10.1078/0044-5231-00032|bibcode=2001ZooAn.240..247B |hdl=11380/304261|hdl-access=free}}</ref>
*'''tetraploid''' (four sets; 4''x''), for example, [[Plains viscacha rat]], [[Salmonidae]] fish,<ref name="McPhail-1997">{{cite book |doi=10.1007/978-1-4615-6375-4_4 |chapter=The Origin and Speciation of Oncorhynchus Revisited |title=Pacific Salmon & Their Ecosystems |date=1997 |last1=McPhail |first1=J. D. |pages=29–38 |isbn=978-0-412-98691-8 }}</ref> the cotton ''[[Gossypium hirsutum]]''<ref>{{cite journal | vauthors = Adams KL, Wendel JF | title = Polyploidy and genome evolution in plants | journal = Current Opinion in Plant Biology | volume = 8 | issue = 2 | pages = 135–141 | date = April 2005 | pmid = 15752992 | doi = 10.1016/j.pbi.2005.01.001 | bibcode = 2005COPB....8..135A }}</ref>
*'''pentaploid''' (five sets; 5''x''), for example Kenai Birch (''[[Betula kenaica]]'')
*'''hexaploid''' (six sets; 6''x''), for example some species of [[wheat]],<ref>{{cite book |doi=10.1016/B978-0-12-817563-7.00028-3 |chapter=Wide hybridization |title=Plant Breeding and Cultivar Development |date=2021 |last1=Singh |first1=Dhan Pal |last2=Singh |first2=Asheesh K. |last3=Singh |first3=Arti |pages=159–178 |isbn=978-0-12-817563-7 }}</ref> [[kiwifruit]]<ref name="Crowhurst-1992">{{cite journal |last1=Crowhurst |first1=Ross N. |last2=Whittaker |first2=D. |last3=Gardner |first3=R. C. |title=The Genetic Origin of Kiwifruit |journal=Acta Horticulturae |date=April 1992 |issue=297 |pages=61–62 |doi=10.17660/ActaHortic.1992.297.5 }}</ref>
*'''heptaploid''' or '''septaploid''' (seven sets; 7''x''), for example some cultured [[Siberian sturgeon]]<ref>{{cite journal |last1=Havelka |first1=Miloš |last2=Bytyutskyy |first2=Dmytro |last3=Symonová |first3=Radka |last4=Ráb |first4=Petr |last5=Flajšhans |first5=Martin |title=The second highest chromosome count among vertebrates is observed in cultured sturgeon and is associated with genome plasticity |journal=Genetics Selection Evolution |date=11 February 2016 |volume=48 |article-number=12 |doi=10.1186/s12711-016-0194-0 |doi-access=free |pmid=26867760 |pmc=4751722 }}</ref>
*'''octaploid''' or '''octoploid''', (eight sets; 8''x''), for example ''[[Acipenser]]'' (genus of [[sturgeon]] fish), [[dahlia]]s
*'''decaploid''' (ten sets; 10''x''), for example certain [[Fragaria|strawberries]]
*'''hendecaploid''' or '''undecaploid''' (eleven sets; 11''x''), for example some ''[[Lepidium]]''{{Hair space}}<ref>{{cite journal |last1= Dierschke|first1= Tom|last2= Mandáková|first2= Terezie|last3= Mummenhoff|first3 = Klaus|date= 9 July 2009|title= A Bicontinental Origin of Polyploid Australian/New Zealand ''Lepidium'' Species (Brassicaceae)? Evidence from Genomic ''in situ'' Hybridization|journal= Annals of Botany|volume= 104|issue= 4|pages= 681–688|doi= 10.1093/aob/mcp161|pmid= 19589857|pmc= 2729636}}</ref> species and [[rose]] cultivars
*'''dodecaploid''' or '''duodecaploid''' (twelve sets; 12''x''), for example the plants ''[[Celosia argentea]]'' and ''[[Spartina anglica]]''{{Hair space}}<ref>{{cite journal| vauthors = Aïnouche ML, Fortune PM, Salmon A, Parisod C, Grandbastien MA, Fukunaga K, Ricou M, Misset MT | display-authors = 6 |year=2008|title=Hybridization, polyploidy and invasion: Lessons from ''Spartina'' (Poaceae)|journal=Biological Invasions|volume=11|issue=5|pages=1159–1173|doi=10.1007/s10530-008-9383-2 }}</ref> or the amphibian ''[[Xenopus ruwenzoriensis]]''.
*'''tetratetracontaploid''' (forty-four sets; 44''x''), for example [[Morus nigra|black mulberry]]<ref>
:{{ cite journal | issue = 10 | year = 2017 | volume = 7 | vauthors = Hussain F, Rana Z, Shafique H, Malik A, Hussain Z | pages = 950–956 | publisher = [[Medknow]] | title = Phytopharmacological potential of different species of Morus alba and their bioactive phytochemicals: A review | journal = [[Asian Pacific Journal of Tropical Biomedicine]] | doi = 10.1016/j.apjtb.2017.09.015 | issn = 2221-1691 | doi-access = free }}
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:{{ cite book | year = 2018 | publisher = [[Springer International Publishing AG]] | vauthors = Al-Khayri JM, Jain SM, Johnson DV | veditors = Al-Khayri JM, Jain SM, Johnson DV | pages = 89–130 | url=| title = Advances in Plant Breeding Strategies: Fruits | volume = 2 | doi = 10.1007/978-3-319-91944-7 | isbn = 978-3-319-91943-0 }}
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:This review and book cite this research.
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:{{cite journal | vauthors = Zeng Q, Chen H, Zhang C, Han M, Li T, Qi X, Xiang Z, He N | display-authors = 6 | title = Definition of Eight Mulberry Species in the Genus ''Morus'' by Internal Transcribed Spacer-Based Phylogeny | journal = PLOS ONE | volume = 10 | issue = 8 | article-number = e0135411 | date = 2015 | pmid = 26266951 | doi = 10.1371/journal.pone.0135411 | pmc = 4534381 | bibcode = 2015PLoSO..1035411Z | doi-access = free }}
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=== Classification ===

==== Autopolyploidy ====
'''Autopolyploids''' are polyploids with multiple chromosome sets derived from a single [[taxon]].

Two examples of natural autopolyploids are the piggyback plant, ''[[Tolmiea menziesii|Tolmiea menzisii]]''<ref>{{Cite journal| vauthors = Soltis DE |date=October 1984 |title=Autopolyploidy in ''Tolmiea menziesii'' (Saxifragaceae)|journal=American Journal of Botany|volume=71|issue=9|pages=1171–1174|doi=10.2307/2443640|jstor=2443640}}</ref> and the white sturgeon, ''[[White sturgeon|Acipenser transmontanum]]''.<ref>{{Cite journal| vauthors = Drauch Schreier A, Gille D, Mahardja B, May B |date= November 2011|title=Neutral markers confirm the octoploid origin and reveal spontaneous autopolyploidy in white sturgeon, ''Acipenser transmontanus''|journal=Journal of Applied Ichthyology|language=en|volume=27|pages=24–33|doi=10.1111/j.1439-0426.2011.01873.x|issn=1439-0426|doi-access=free|bibcode= 2011JApIc..27...24D}}</ref> Most instances of autopolyploidy result from the fusion of unreduced (2''n'') gametes, which results in either triploid (''n'' + 2''n'' = 3''n'') or tetraploid (2''n'' + 2''n'' = 4''n'') offspring.<ref name="Bretagnolle-1995">{{cite journal | vauthors = Bretagnolle F, Thompson JD | title = Gametes with the somatic chromosome number: mechanisms of their formation and role in the evolution of autopolyploid plants | journal = The New Phytologist | volume = 129 | issue = 1 | pages = 1–22 | date = January 1995 | pmid = 33874422 | doi = 10.1111/j.1469-8137.1995.tb03005.x | bibcode = 1995NewPh.129....1B | doi-access = free }}</ref> Triploid offspring are typically sterile (as in the phenomenon of [[triploid block]]), but in some cases they may produce high proportions of unreduced gametes and thus aid the formation of tetraploids. This pathway to tetraploidy is referred to as the ''triploid bridge''.<ref name="Bretagnolle-1995" /> Triploids may also persist through [[asexual reproduction]]. In fact, stable autotriploidy in plants is often associated with [[Apomixis|apomictic]] mating systems.<ref>{{Cite journal| vauthors = Müntzing A |date=March 1936|title=The Evolutionary Significance of Autopolyploidy|journal=Hereditas|language=en|volume=21|issue=2–3|pages=363–378|doi=10.1111/j.1601-5223.1936.tb03204.x|issn=1601-5223|doi-access=free}}</ref> In agricultural systems, autotriploidy can result in seedlessness, as in [[watermelon]]s and [[banana]]s.<ref>{{cite journal | vauthors = Varoquaux F, Blanvillain R, Delseny M, Gallois P | title = Less is better: new approaches for seedless fruit production | journal = Trends in Biotechnology | volume = 18 | issue = 6 | pages = 233–242 | date = June 2000 | pmid = 10802558 | doi = 10.1016/s0167-7799(00)01448-7 }}</ref> Triploidy is also utilized in salmon and trout farming to induce sterility.<ref>{{Cite journal| vauthors = Cotter D, O'Donovan V, O'Maoiléidigh N, Rogan G, Roche N, Wilkins NP |date=June 2000|title=An evaluation of the use of triploid Atlantic salmon (''Salmo salar'' L.) in minimising the impact of escaped farmed salmon on wild populations|journal=Aquaculture|volume=186|issue=1–2|pages=61–75|doi=10.1016/S0044-8486(99)00367-1|bibcode=2000Aquac.186...61C }}</ref><ref>{{Cite journal| vauthors = Lincoln RF, Scott AP |year=1983|title=Production of all-female triploid rainbow trout|journal=Aquaculture|language=en|volume=30|issue=1–4|pages=375–380|doi=10.1016/0044-8486(83)90179-5|bibcode=1983Aquac..30..375L }}</ref>

Rarely, autopolyploids arise from spontaneous, somatic genome doubling, which has been observed in apple (''Malus domesticus'') [[Sport (botany)|bud sports]].<ref>{{Cite journal| vauthors = Dermen H |date=May 1951|title=Tetraploid and Diploid Adventitious Shoots: From a Giant Sport of McIntosh Apple|journal=Journal of Heredity|volume=42|issue=3|pages=145–149|doi=10.1093/oxfordjournals.jhered.a106189 }}</ref> This is also the most common pathway of artificially induced polyploidy, where methods such as [[Somatic fusion|protoplast fusion]] or treatment with [[colchicine]], [[oryzalin]] or [[mitotic inhibitor]]s are used to disrupt normal [[Mitosis|mitotic]] division, which results in the production of polyploid cells. This process can be useful in plant breeding, especially when attempting to introgress germplasm across ploidal levels.<ref>{{cite book |doi=10.1002/9780470380130.ch3 |chapter=Enhancing Crop Gene Pools with Beneficial Traits Using Wild Relatives |title=Plant Breeding Reviews |date=2007 |last1=Dwivedi |first1=Sangam L. |last2=Upadhyaya |first2=Hari D. |last3=Stalker |first3=H. Thomas |last4=Blair |first4=Matthew W. |last5=Bertioli |first5=David J. |last6=Nielen |first6=Stephan |last7=Ortiz |first7=Rodomiro |pages=179–230 |isbn=978-0-470-17152-3 |chapter-url=http://oar.icrisat.org/2546/1/Enhancing_Crop_Gene_Pools.pdf }}</ref>

Autopolyploids possess at least three [[homologous chromosome]] sets, which can lead to high rates of multivalent pairing during [[meiosis]] (particularly in recently formed autopolyploids, also known as neopolyploids) and an associated decrease in fertility due to the production of [[Aneuploidy|aneuploid]] gametes.<ref name="Justin-2002">{{Cite journal| vauthors = Justin R |date=January 2002|title=Neopolyploidy in Flowering Plants|journal=Annual Review of Ecology and Systematics|volume=33|issue=1|pages=589–639|doi=10.1146/annurev.ecolsys.33.010802.150437 |bibcode=2002AnRES..33..589R }}</ref> Natural or artificial selection for fertility can quickly stabilize meiosis in autopolyploids by restoring bivalent pairing during meiosis. Rapid adaptive evolution of the meiotic machinery, resulting in reduced levels of multivalents (and therefore stable autopolyploid meiosis) has been documented in ''Arabidopsis arenosa''<ref>{{Cite journal |last1=Yant |first1=Levi |last2=Hollister |first2=Jesse D. |last3=Wright |first3=Kevin M. |last4=Arnold |first4=Brian J. |last5=Higgins |first5=James D. |last6=Franklin |first6=F. Chris H. |last7=Bomblies |first7=Kirsten |date=November 2013 |title=Meiotic Adaptation to Genome Duplication in Arabidopsis arenosa |url=|journal=Current Biology |volume=23 |issue=21 |pages=2151–2156 |doi=10.1016/j.cub.2013.08.059 |issn=0960-9822 |pmc=3859316 |pmid=24139735|bibcode=2013CBio...23.2151Y }}</ref> and ''Arabidopsis lyrata'',<ref name="auto1"/> with specific adaptive alleles of these species shared between only the evolved polyploids.<ref name="auto1"/><ref>{{Cite journal |last1=Seear |first1=Paul J. |last2=France |first2=Martin G. |last3=Gregory |first3=Catherine L. |last4=Heavens |first4=Darren |last5=Schmickl |first5=Roswitha |last6=Yant |first6=Levi |last7=Higgins |first7=James D. |date=2020-07-15 |editor-last=Grelon |editor-first=Mathilde |title=A novel allele of ASY3 is associated with greater meiotic stability in autotetraploid Arabidopsis lyrata |journal=PLOS Genetics |language=en |volume=16 |issue=7 |article-number=e1008900 |doi=10.1371/journal.pgen.1008900 |doi-access=free |issn=1553-7404 |pmc=7392332 |pmid=32667955}}</ref> 

The high degree of [[Homology (biology)|homology]] among duplicated chromosomes causes autopolyploids to display [[polysomic inheritance]].<ref>{{cite journal | vauthors = Parisod C, Holderegger R, Brochmann C | title = Evolutionary consequences of autopolyploidy | journal = The New Phytologist | volume = 186 | issue = 1 | pages = 5–17 | date = April 2010 | pmid = 20070540 | doi = 10.1111/j.1469-8137.2009.03142.x | bibcode = 2010NewPh.186....5P | doi-access =  }}</ref> This trait is often used as a diagnostic criterion to distinguish autopolyploids from allopolyploids, which commonly display disomic inheritance after they progress past the neopolyploid stage.<ref name="Le Comber-2010">{{cite journal | vauthors = Le Comber SC, Ainouche ML, Kovarik A, Leitch AR | title = Making a functional diploid: from polysomic to disomic inheritance | journal = The New Phytologist | volume = 186 | issue = 1 | pages = 113–122 | date = April 2010 | pmid = 20028473 | doi = 10.1111/j.1469-8137.2009.03117.x | bibcode = 2010NewPh.186..113L | doi-access =  }}</ref> While most polyploid species are unambiguously characterized as either autopolyploid or allopolyploid, these categories represent the ends of a spectrum of divergence between parental subgenomes. Polyploids that fall between these two extremes, which are often referred to as segmental allopolyploids, may display intermediate levels of polysomic inheritance that vary by locus.<ref>{{Cite book| vauthors = Stebbins GL |title=Types of Polyploids: Their Classification and Significance|year=1947|isbn=978-0-12-017601-4|series=Advances in Genetics|volume=1|pages=403–429|language=en|doi=10.1016/s0065-2660(08)60490-3|pmid=20259289}}</ref><ref>{{Cite book| vauthors = Stebbins GL |title=Variation and Evolution in Plants|publisher=Oxford University Press|year=1950}}{{page needed|date=March 2019}}</ref>

About half of all polyploids are thought to be the result of autopolyploidy,<ref>{{Cite journal| vauthors = Ramsey J, Schemske DW |date= January 1998 |title=Pathways, Mechanisms, and Rates of Polyploid Formation in Flowering Plants|journal=Annual Review of Ecology and Systematics|volume=29|issue=1|pages=467–501|doi=10.1146/annurev.ecolsys.29.1.467 |bibcode= 1998AnRES..29..467R }}</ref><ref>{{cite journal | vauthors = Barker MS, Arrigo N, Baniaga AE, Li Z, Levin DA | title = On the relative abundance of autopolyploids and allopolyploids | journal = The New Phytologist | volume = 210 | issue = 2 | pages = 391–398 | date = April 2016 | pmid = 26439879 | doi = 10.1111/nph.13698 | bibcode = 2016NewPh.210..391B | doi-access = free }}</ref> although many factors make this proportion hard to estimate.<ref>{{cite journal | vauthors = Doyle JJ, Sherman-Broyles S | title = Double trouble: taxonomy and definitions of polyploidy | journal = The New Phytologist | volume = 213 | issue = 2 | pages = 487–493 | date = January 2017 | pmid = 28000935 | doi = 10.1111/nph.14276 | bibcode = 2017NewPh.213..487D | doi-access = free }}</ref>

==== Allopolyploidy ====
'''Allopolyploids''' or '''amphipolyploids''' or '''heteropolyploids''' are polyploids with chromosomes derived from two or more diverged taxa.

As in autopolyploidy, this primarily occurs through the fusion of unreduced (2''n'') gametes, which can take place before or after [[Hybrid (biology)|hybridization]]. In the former case, unreduced gametes from each diploid taxon – or reduced gametes from two autotetraploid taxa – combine to form allopolyploid offspring. In the latter case, one or more diploid [[F1 hybrid|F<sub>1</sub> hybrids]] produce unreduced gametes that fuse to form allopolyploid progeny.<ref name="Ramsey-1998">{{Cite journal| vauthors = Ramsey J |date=January 1998|title=Pathways, Mechanisms, and Rates of Polyploid Formation in Flowering Plants|journal=Annual Review of Ecology and Systematics|volume=29|issue=1|pages=467–501|doi=10.1146/annurev.ecolsys.29.1.467 |bibcode=1998AnRES..29..467R }}</ref> Hybridization followed by genome duplication may be a more common path to allopolyploidy because F<sub>1</sub> hybrids between taxa often have relatively high rates of unreduced gamete formation – divergence between the genomes of the two taxa result in abnormal pairing between [[homoeologous]] chromosomes or [[nondisjunction]] during meiosis.<ref name="Ramsey-1998" /> In this case, allopolyploidy can actually restore normal, [[Bivalent (genetics)|bivalent]] meiotic pairing by providing each homoeologous chromosome with its own homologue. If divergence between homoeologous chromosomes is even across the two subgenomes, this can theoretically result in rapid restoration of bivalent pairing and disomic inheritance following allopolyploidization. However multivalent pairing is common in many recently formed allopolyploids, so it is likely that the majority of meiotic stabilization occurs gradually through selection.<ref name="Justin-2002" /><ref name="Le Comber-2010" />

Because pairing between homoeologous chromosomes is rare in established allopolyploids, they may benefit from fixed [[heterozygosity]] of homoeologous alleles.<ref name="Comai-2005">{{cite journal | vauthors = Comai L | title = The advantages and disadvantages of being polyploid | journal = Nature Reviews. Genetics | volume = 6 | issue = 11 | pages = 836–846 | date = November 2005 | pmid = 16304599 | doi = 10.1038/nrg1711 }}</ref> In certain cases, such heterozygosity can have beneficial [[Heterosis|heterotic]] effects, either in terms of fitness in natural contexts or desirable traits in agricultural contexts. This could partially explain the prevalence of allopolyploidy among crop species. Both bread [[wheat]] and [[triticale]] are examples of an allopolyploids with six chromosome sets. [[Cotton]], [[peanut]], and [[quinoa]] are allotetraploids with multiple origins. In [[Brassicaceae|Brassicaceous]] crops, the [[Triangle of U]] describes the relationships between the three common diploid Brassicas (''[[Brassica oleracea|B. oleracea]], [[Brassica rapa|B. rapa]],'' and ''[[Brassica nigra|B. nigra]]'') and three allotetraploids (''[[Rapeseed|B. napus]], [[Brassica juncea|B. juncea]],'' and ''[[Brassica carinata|B. carinata]]'') derived from hybridization among the diploid species. A similar relationship exists between three diploid species of ''[[Tragopogon]]'' (''[[Tragopogon dubius|T. dubius]], [[Tragopogon pratensis|T. pratensis]],'' and ''[[Tragopogon porrifolius|T. porrifolius]]'') and two allotetraploid species (''[[Tragopogon mirus|T. mirus]]'' and ''[[Tragopogon miscellus|T. miscellus]]'').<ref>{{Cite journal| vauthors = Ownbey M |date=January 1950|title=Natural Hybridization and Amphiploidy in the Genus Tragopogon|journal=American Journal of Botany|volume=37|issue=7|pages=487–499|doi=10.2307/2438023|jstor=2438023}}</ref> Complex patterns of allopolyploid evolution have also been observed in animals, as in the frog genus ''[[Xenopus]].''<ref>{{cite journal | vauthors = Schmid M, Evans BJ, Bogart JP | title = Polyploidy in Amphibia | journal = Cytogenetic and Genome Research | volume = 145 | issue = 3–4 | pages = 315–330 | year = 2015 | pmid = 26112701 | doi = 10.1159/000431388 | doi-access = free }}</ref>

==== Aneuploid ====
{{main|Aneuploidy}}
Organisms in which a particular chromosome, or chromosome segment, is under- or over-represented are said to be [[Aneuploidy|aneuploid]] (from the Greek words meaning "not", "good", and "fold"). Aneuploidy refers to a numerical change in part of the chromosome set, whereas polyploidy refers to a numerical change in the whole set of chromosomes.<ref name="Griffiths-1999">{{cite book| vauthors = Griffiths AJ |title=An Introduction to genetic analysis|publisher=W.H. Freeman|year=1999|isbn=978-0-7167-3520-5|location=San Francisco, CA}}{{page needed|date=September 2013}}</ref>

==== Endopolyploidy ====
Polyploidy occurs in some tissues of animals that are otherwise diploid, such as human [[muscle]] tissues.<ref name="Parmacek-2009">{{cite journal | vauthors = Parmacek MS, Epstein JA | title = Cardiomyocyte renewal | journal = The New England Journal of Medicine | volume = 361 | issue = 1 | pages = 86–88 | date = July 2009 | pmid = 19571289 | pmc = 4111249 | doi = 10.1056/NEJMcibr0903347 }}</ref> This is known as '''endopolyploidy'''. Species whose cells do not have nuclei, that is, [[prokaryotes]], may be polyploid, as seen in the large [[bacterium]] ''[[Epulopiscium fishelsoni]]''.<ref>{{cite journal | vauthors = Mendell JE, Clements KD, Choat JH, Angert ER | title = Extreme polyploidy in a large bacterium | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 105 | issue = 18 | pages = 6730–6734 | date = May 2008 | pmid = 18445653 | pmc = 2373351 | doi = 10.1073/pnas.0707522105 | doi-access = free | bibcode = 2008PNAS..105.6730M }}</ref> Hence [[ploidy]] is defined with respect to a cell.

==== Monoploid ====
{{main|Monoploidy}}
A monoploid has only one set of chromosomes and the term is usually only applied to cells or organisms that are normally diploid. The more general term for such organisms is [[haploid]].

=== Temporal terms ===

==== Neopolyploidy ====
A polyploid that is newly formed.

==== Mesopolyploidy ====
That has become polyploid in more recent history; it is not as new as a neopolyploid and not as old as a paleopolyploid. It is a middle aged polyploid. Often this refers to whole genome duplication followed by intermediate levels of diploidization.

==== Paleopolyploidy ====
[[File:PaleopolyploidyTree.jpg|upright=1.5|thumb|This [[phylogenetic tree]] shows the relationship between the best-documented instances of [[paleopolyploidy]] in eukaryotes.]]

{{Main|Paleopolyploidy}}
Ancient genome duplications probably occurred in the evolutionary history of all life. Duplication events that occurred long ago in the history of various [[Lineage (evolution)|evolutionary lineages]] can be difficult to detect because of subsequent [[diploidization]] (such that a polyploid starts to behave cytogenetically as a diploid over time) as [[mutation]]s and gene translations gradually make one copy of each chromosome unlike the other copy. Over time, it is also common for duplicated copies of genes to accumulate mutations and become inactive pseudogenes.<ref>{{cite journal | vauthors = Edger PP, Pires JC | title = Gene and genome duplications: the impact of dosage-sensitivity on the fate of nuclear genes | journal = Chromosome Research | volume = 17 | issue = 5 | pages = 699–717 | year = 2009 | pmid = 19802709 | doi = 10.1007/s10577-009-9055-9 | doi-access = free }}</ref>

In many cases, these events can be inferred only through comparing [[DNA sequencing|sequenced genomes]]. Examples of unexpected but recently confirmed ancient genome duplications include [[baker's yeast]] (''[[Saccharomyces cerevisiae]]''), mustard weed/thale cress (''[[Arabidopsis thaliana]]''), [[rice]] (''[[Oryza sativa]]''), and two rounds of whole genome duplication (the [[2R hypothesis]]) in an early [[evolution]]ary [[ancestor]] of the [[vertebrates]] (which includes the [[human]] lineage) and another near the origin of the [[teleost]] [[fishes]].<ref name="Clarke-2016" /> [[Angiosperm]]s ([[flowering plant]]s) have paleopolyploidy in their ancestry. All [[eukaryote]]s probably have experienced a polyploidy event at some point in their evolutionary history.

=== Other similar terms ===

==== Karyotype ====
{{Main|Karyotype}}
A karyotype is the characteristic chromosome complement of a [[eukaryote]] [[species]].<ref>{{cite book| vauthors = White MJ |url= https://archive.org/details/chromosomes01whit |title=The Chromosomes|date=1973|publisher=Chapman & Hall|edition=6th|location=London|page=28|url-access=registration}}</ref><ref>{{cite book| vauthors = Stebbins GL |title=Variation and Evolution in Plants|date=1950|publisher=Columbia University Press|location=New York, NY|chapter=Chapter XII: The Karyotype}}{{page needed|date=September 2013}}</ref> The preparation and study of karyotypes is part of [[cytopathology|cytology]] and, more specifically, [[cytogenetics]].

Although the replication and transcription of DNA is highly standardized in [[eukaryotes]], the same cannot be said for their karyotypes, which are highly variable between species in chromosome number and in detailed organization despite being constructed out of the same macromolecules. In some cases, there is even significant variation within species. This variation provides the basis for a range of studies in what might be called evolutionary cytology.

==== Homoeologous chromosomes ====
{{Main|Homoeology}}
[[Homoeologous chromosome]]s are those brought together following [[Hybrid (biology)|inter-species hybridization]] and [[Allopolyploidy|allopolyploidization]], and whose relationship was completely homologous in an ancestral species. For example, [[Durum#Genealogy|durum wheat]] is the result of the inter-species hybridization of two diploid grass species ''Triticum urartu'' and ''Aegilops speltoides''. Both diploid ancestors had two sets of 7 chromosomes, which were similar in terms of size and genes contained on them. Durum wheat contains a [[Eukaryote hybrid genome|hybrid genome]] with two sets of chromosomes derived from ''Triticum urartu'' and two sets of chromosomes derived from ''Aegilops speltoides''. Each chromosome pair derived from the ''Triticum urartu'' parent is '''homoeologous''' to the opposite chromosome pair derived from the ''Aegilops speltoides'' parent, though each chromosome pair unto itself is '''homologous'''.

== Examples ==

=== Humans ===
[[File:Human karyotype with bands and sub-bands.png|thumb|Schematic [[karyotype|karyogram]] of a human, showing the normal [[diploid]] (that is, non-polyploid) [[karyotype]]. It shows 22 [[homologous chromosome]]s, both the female (XX) and male (XY) versions of the [[sex chromosome]] (bottom right), as well as the [[human mitochondrial genetics|mitochondrial genome]] (to scale at bottom left).{{further|Karyotype}}]]
{{Further|Triploid syndrome}}

True polyploidy rarely occurs in humans, although polyploid cells occur in highly [[Cellular differentiation|differentiated]] tissue, such as liver [[parenchyma]], heart muscle, placenta and in bone marrow.<ref name="Velicky-2018">{{cite journal | vauthors = Velicky P, Meinhardt G, Plessl K, Vondra S, Weiss T, Haslinger P, Lendl T, Aumayr K, Mairhofer M, Zhu X, Schütz B, Hannibal RL, Lindau R, Weil B, Ernerudh J, Neesen J, Egger G, Mikula M, Röhrl C, Urban AE, Baker J, Knöfler M, Pollheimer J | display-authors = 6 | title = Genome amplification and cellular senescence are hallmarks of human placenta development | journal = PLOS Genetics | volume = 14 | issue = 10 | article-number = e1007698 | date = October 2018 | pmid = 30312291 | pmc = 6200260 | doi = 10.1371/journal.pgen.1007698 | doi-access = free }}
</ref><ref>{{cite journal | vauthors = Winkelmann M, Pfitzer P, Schneider W | title = Significance of polyploidy in megakaryocytes and other cells in health and tumor disease | journal = Klinische Wochenschrift | volume = 65 | issue = 23 | pages = 1115–1131 | date = December 1987 | pmid = 3323647 | doi = 10.1007/BF01734832 }}</ref> [[Aneuploidy]] is more common.

Polyploidy occurs in humans in the form of [[Triploid syndrome|triploidy]], with 69 chromosomes (sometimes called 69, XXX), and tetraploidy with 92 chromosomes (sometimes called 92, XXXX). Triploidy, usually due to [[polyspermy]], occurs in about 2–3% of all human pregnancies and ~15% of miscarriages.{{Citation needed|date=November 2009}} The vast majority of triploid conceptions end as a [[miscarriage]]; those that do survive to term typically die shortly after birth. In some cases, survival past birth may be extended if there is [[mixoploidy]] with both a [[diploid]] and a triploid cell population present. There has been one report of a child surviving to the age of seven months with complete triploidy syndrome. He failed to exhibit normal mental or physical neonatal development, and died from a ''[[Pneumocystis carinii]]'' infection, which indicates a weak immune system.<ref>{{cite web|url=https://rarediseases.org/rare-diseases/triploidy/|title=Triploidy|publisher=National Organization for Rare Disorders|language=en-US|access-date=2018-12-23}}</ref>

Triploidy may be the result of either [[digyny]] (the extra haploid set is from the mother) or [[diandry]] (the extra haploid set is from the father). Diandry is mostly caused by reduplication of the paternal haploid set from a single sperm, but may also be the consequence of dispermic (two sperm) [[fertilization]] of the egg.<ref name="Baker-2006">{{cite book | vauthors = Baker P, Monga A, Baker P |title=Gynaecology by Ten Teachers |publisher=Arnold |location=London |year=2006 |isbn=978-0-340-81662-2 |url-access=registration |url=https://archive.org/details/gynaecology0000unse }}</ref> Digyny is most commonly caused by either failure of one meiotic division during oogenesis leading to a diploid [[oocyte]] or failure to extrude one [[polar body]] from the [[oocyte]]. Diandry appears to predominate among early [[miscarriage]]s, while digyny predominates among triploid zygotes that survive into the fetal period.<ref>{{cite journal | vauthors = Brancati F, Mingarelli R, Dallapiccola B | title = Recurrent triploidy of maternal origin | journal = European Journal of Human Genetics | volume = 11 | issue = 12 | pages = 972–974 | date = December 2003 | pmid = 14508508 | doi = 10.1038/sj.ejhg.5201076 | doi-access = free }}</ref> However, among early miscarriages, digyny is also more common in those cases less than {{frac|8|1|2}} weeks gestational age or those in which an embryo is present. There are also two distinct [[phenotype]]s in triploid [[placenta]]s and [[fetus]]es that are dependent on the origin of the extra [[haploid]] set. In digyny, there is typically an asymmetric poorly grown [[fetus]], with marked [[adrenal]] [[hypoplasia]] and a very small [[placenta]].<ref name="Wick-2013">{{cite journal | vauthors = Wick JB, Johnson KJ, O'Brien J, Wick MJ | title = Second-trimester diagnosis of triploidy: a series of four cases | journal = AJP Reports | volume = 3 | issue = 1 | pages = 37–40 | date = May 2013 | pmid = 23943708 | pmc = 3699153 | doi = 10.1055/s-0032-1331378 }}</ref> In diandry, a partial [[hydatidiform mole]] develops.<ref name="Baker-2006" /> These parent-of-origin effects reflect the effects of [[imprinting (genetics)|genomic imprinting]].{{citation needed|date=December 2010}}

Complete tetraploidy is more rarely diagnosed than triploidy, but is observed in 1–2% of early miscarriages. However, some tetraploid cells are commonly found in chromosome analysis at [[prenatal diagnosis]] and these are generally considered 'harmless'. It is not clear whether these tetraploid cells simply tend to arise during ''in vitro'' cell culture or whether they are also present in placental cells ''in vivo''. There are, at any rate, very few clinical reports of fetuses/infants diagnosed with tetraploidy mosaicism.

[[Mixoploidy]] is quite commonly observed in human preimplantation embryos and includes haploid/diploid as well as diploid/tetraploid mixed cell populations. It is unknown whether these embryos fail to implant and are therefore rarely detected in ongoing pregnancies or if there is simply a selective process favoring the diploid cells.

===Other animals===
Examples in animals are more common in non-vertebrates<ref>{{cite journal | vauthors = Otto SP, Whitton J | title = Polyploid incidence and evolution | journal = Annual Review of Genetics | volume = 34 | issue = 1 | pages = 401–437 | year = 2000 | pmid = 11092833 | doi = 10.1146/annurev.genet.34.1.401 | citeseerx = 10.1.1.323.1059 }}</ref> such as [[flatworm]]s, [[leech]]es, and [[brine shrimp]]. Polyploidy also occurs commonly in amphibians; for example the biomedically important genus ''[[Xenopus]]'' contains many different species with as many as 12 sets of chromosomes (dodecaploid).<ref>{{cite journal |doi=10.1093/sysbio/42.4.476 |title=''Xenopus laevis'' as a Model Organism |year=1993 | vauthors = Cannatella DC, De Sa RO |journal=Society of Systematic Biologists |volume=42 |issue=4|pages=476–507}}</ref> Polyploid lizards are also quite common. Most are sterile and reproduce by [[parthenogenesis]];{{citation needed|date=August 2013}} others, like ''[[Liolaemus chiliensis]]'', maintain sexual reproduction. Polyploid [[mole salamanders]] (mostly triploids) are all female and reproduce by [[kleptogenesis]],<ref name="Bogart-2007">{{cite journal | vauthors = Bogart JP, Bi K, Fu J, Noble DW, Niedzwiecki J | title = Unisexual salamanders (genus Ambystoma) present a new reproductive mode for eukaryotes | journal = Genome | volume = 50 | issue = 2 | pages = 119–136 | date = February 2007 | pmid = 17546077 | doi = 10.1139/g06-152 }}</ref> "stealing" [[spermatophore]]s from diploid males of related species to trigger egg development but not incorporating the males' DNA into the offspring.

While some tissues of mammals, such as [[Parenchyma|parenchymal]] liver cells, are polyploid,<ref>{{cite journal | vauthors = Epstein CJ | title = Cell size, nuclear content, and the development of polyploidy in the Mammalian liver | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 57 | issue = 2 | pages = 327–334 | date = February 1967 | pmid = 16591473 | pmc = 335509 | doi = 10.1073/pnas.57.2.327 | bibcode = 1967PNAS...57..327E | doi-access = free }}</ref><ref>{{cite journal | vauthors = Donne R, Saroul-Aïnama M, Cordier P, Celton-Morizur S, Desdouets C | title = Polyploidy in liver development, homeostasis and disease | journal = Nature Reviews. Gastroenterology & Hepatology | volume = 17 | issue = 7 | pages = 391–405 | date = July 2020 | pmid = 32242122 | doi = 10.1038/s41575-020-0284-x | url = https://inserm.hal.science/inserm-02992166 }}</ref> rare instances of polyploid [[mammals]] are known, but most often result in [[prenatal]] death. An [[Octodontidae|octodontid]] [[rodent]] of [[Argentina]]'s harsh [[desert]] regions, known as the [[plains viscacha rat]] (''Tympanoctomys barrerae'') has been reported as an exception to this 'rule'.<ref>{{cite journal | vauthors = Gallardo MH, González CA, Cebrián I | title = Molecular cytogenetics and allotetraploidy in the red vizcacha rat, Tympanoctomys barrerae (Rodentia, Octodontidae) | journal = Genomics | volume = 88 | issue = 2 | pages = 214–221 | date = August 2006 | pmid = 16580173 | doi = 10.1016/j.ygeno.2006.02.010 | doi-access = free | hdl = 10533/178085 | hdl-access = free }}</ref> However, careful analysis using chromosome paints shows that there are only two copies of each chromosome in ''T. barrerae'', not the four expected if it were truly a tetraploid.<ref name="Svartman-2005">{{cite journal | vauthors = Svartman M, Stone G, Stanyon R | title = Molecular cytogenetics discards polyploidy in mammals | journal = Genomics | volume = 85 | issue = 4 | pages = 425–430 | date = April 2005 | pmid = 15780745 | doi = 10.1016/j.ygeno.2004.12.004 }}</ref> This rodent is not a [[rat]], but kin to [[guinea pig]]s and [[chinchilla]]s. Its "new" diploid (2''n'') number is 102 and so its cells are roughly twice normal size. Its closest living relation is ''[[Octomys mimax]]'', the [[Andes|Andean]] Viscacha-Rat of the same family, whose 2''n'' = 56. It was therefore surmised that an ''Octomys''-like ancestor produced tetraploid (i.e., 2''n'' = 4''x'' = 112) offspring that were, by virtue of their doubled chromosomes, reproductively isolated from their parents.

Polyploidy was induced in fish by [[Har Swarup]] (1956) using a cold-shock treatment of the eggs close to the time of fertilization, which produced triploid embryos that successfully matured.<ref>{{cite journal |doi=10.1038/1781124a0 |title=Production of Heteroploidy in the Three-Spined Stickleback, ''Gasterosteus aculeatus'' (L.) |year=1956 | vauthors = Swarup H |journal=Nature |volume=178 |issue=4542 |pages=1124–1125|bibcode=1956Natur.178.1124S }}</ref><ref>{{cite journal |doi=10.1007/BF02984740 |title=Production of triploidy in ''Gasterosteus aculeatus'' (L.) |year=1959 | vauthors = Swarup H |journal=Journal of Genetics |volume=56 |issue=2 |pages=129–142 }}</ref> Cold or heat shock has also been shown to result in unreduced amphibian gametes, though this occurs more commonly in eggs than in sperm.<ref>{{cite journal | vauthors = Mable BK, Alexandrou MA, Taylor MI |doi=10.1111/j.1469-7998.2011.00829.x |title=Genome duplication in amphibians and fish: an extended synthesis |year=2011 |journal=Journal of Zoology |volume=284 |issue=3 |pages=151–182 |doi-access=free }}</ref> [[John Gurdon]] (1958) transplanted intact nuclei from somatic cells to produce diploid eggs in the frog, ''[[Xenopus]]'' (an extension of the work of Briggs and King in 1952) that were able to develop to the tadpole stage.<ref name="Nobel Foundation-2012">{{cite press release |title=Nobel Prize in Physiology or Medicine 2012 awarded for discovery that mature cells can be reprogrammed to become pluripotent |url=https://www.sciencedaily.com/releases/2012/10/121008082955.htm |work=ScienceDaily |publisher=Nobel Foundation |date=8 October 2012 }}</ref> The British scientist [[J. B. S. Haldane]] hailed the work for its potential medical applications and, in describing the results, became one of the first to use the word "[[Cloning|clone]]" in reference to animals. Later work by [[Shinya Yamanaka]] showed how mature cells can be reprogrammed to become pluripotent, extending the possibilities to non-stem cells. Gurdon and Yamanaka were jointly awarded the Nobel Prize in 2012 for this work.<ref name="Nobel Foundation-2012" />

==== Fish ====
A polyploidy event occurred within the stem lineage of the [[teleost]] fish.<ref name="Clarke-2016">{{cite journal | vauthors = Clarke JT, Lloyd GT, Friedman M | title = Little evidence for enhanced phenotypic evolution in early teleosts relative to their living fossil sister group | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 113 | issue = 41 | pages = 11531–11536 | date = October 2016 | pmid = 27671652 | pmc = 5068283 | doi = 10.1073/pnas.1607237113 | bibcode = 2016PNAS..11311531C | doi-access = free }}</ref> Some fish which include the [[salmonids]] and many [[cyprinids]] (i.e. [[carp]]) exhibit stable polyploidy, where entire species consist entirely of polyploid individuals. Some fish{{Example needed|s|date=September 2025}} have as many as 400 chromosomes.<ref name="Smith-2012">{{cite journal | vauthors = Smith LE | title = A suggestion to the medical librarians. 1920 | journal = Journal of the Medical Library Association | volume = 100 | issue = 4 Suppl | pages = B | date = October 2012 | pmid = 23509424 | doi = 10.1023/B:RFBF.0000033049.00668.fe | pmc = 3571666 }}</ref>

=== Plants ===
[[File:Polyploidization.svg|right|thumb|[[Speciation]] via polyploidy: A [[diploid]] cell undergoes failed [[meiosis]], producing diploid [[gamete]]s, which self-fertilize to produce a tetraploid [[zygote]].]]

Polyploidy is frequent in plants, some estimates suggesting that 30–80% of living plant species are polyploid, and many lineages show evidence of ancient polyploidy ([[paleopolyploidy]]) in their genomes.<ref name="Meyers-2006">{{cite journal | vauthors = Meyers LA, Levin DA | title = On the abundance of polyploids in flowering plants | journal = Evolution; International Journal of Organic Evolution | volume = 60 | issue = 6 | pages = 1198–1206 | date = June 2006 | pmid = 16892970 | doi = 10.1111/j.0014-3820.2006.tb01198.x | doi-access = free }}</ref><ref name="Rieseberg-2007">{{cite journal | vauthors = Rieseberg LH, Willis JH | title = Plant speciation | journal = Science | volume = 317 | issue = 5840 | pages = 910–914 | date = August 2007 | pmid = 17702935 | pmc = 2442920 | doi = 10.1126/science.1137729 | bibcode = 2007Sci...317..910R }}</ref><ref name="Otto-2007">{{cite journal | vauthors = Otto SP | title = The evolutionary consequences of polyploidy | journal = Cell | volume = 131 | issue = 3 | pages = 452–462 | date = November 2007 | pmid = 17981114 | doi = 10.1016/j.cell.2007.10.022 | doi-access = free }}</ref><ref>{{cite journal | title = One thousand plant transcriptomes and the phylogenomics of green plants | journal = Nature | volume = 574 | issue = 7780 | pages = 679–685 | date = October 2019 | pmid = 31645766 | pmc = 6872490 | doi = 10.1038/s41586-019-1693-2 | author1 = One Thousand Plant Transcriptomes Initiative }}</ref> Huge explosions in [[angiosperm]] species diversity appear to have coincided with the timing of ancient genome duplications shared by many species.<ref>{{cite journal | vauthors = De Bodt S, Maere S, Van de Peer Y | title = Genome duplication and the origin of angiosperms | journal = Trends in Ecology & Evolution | volume = 20 | issue = 11 | pages = 591–597 | date = November 2005 | pmid = 16701441 | doi = 10.1016/j.tree.2005.07.008 }}</ref> It has been established that 15% of angiosperm and 31% of fern [[speciation]] events are accompanied by ploidy increase.<ref name="Wood-2009">{{cite journal | vauthors = Wood TE, Takebayashi N, Barker MS, Mayrose I, Greenspoon PB, Rieseberg LH | title = The frequency of polyploid speciation in vascular plants | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 106 | issue = 33 | pages = 13875–13879 | date = August 2009 | pmid = 19667210 | pmc = 2728988 | doi = 10.1073/pnas.0811575106 | doi-access = free | bibcode = 2009PNAS..10613875W | jstor = 40484335 }}</ref>

Polyploid plants can arise spontaneously in nature by several mechanisms, including meiotic or mitotic failures, and fusion of unreduced (2''n'') gametes.<ref name="Comai-2005"/> Both autopolyploids (e.g. potato<ref name="Xu-2011">{{cite journal | vauthors = Xu X, Pan S, Cheng S, Zhang B, Mu D, Ni P, Zhang G, Yang S, Li R, Wang J, Orjeda G, Guzman F, Torres M, Lozano R, Ponce O, Martinez D, De la Cruz G, Chakrabarti SK, Patil VU, Skryabin KG, Kuznetsov BB, Ravin NV, Kolganova TV, Beletsky AV, Mardanov AV, Di Genova A, Bolser DM, Martin DM, Li G, Yang Y, Kuang H, Hu Q, Xiong X, Bishop GJ, Sagredo B, Mejía N, Zagorski W, Gromadka R, Gawor J, Szczesny P, Huang S, Zhang Z, Liang C, He J, Li Y, He Y, Xu J, Zhang Y, Xie B, Du Y, Qu D, Bonierbale M, Ghislain M, Herrera M, Giuliano G, Pietrella M, Perrotta G, Facella P, O'Brien K, Feingold SE, Barreiro LE, Massa GA, Diambra L, Whitty BR, Vaillancourt B, Lin H, Massa AN, Geoffroy M, Lundback S, DellaPenna D, Buell CR, Sharma SK, Marshall DF, Waugh R, Bryan GJ, Destefanis M, Nagy I, Milbourne D, Thomson SJ, Fiers M, Jacobs JM, Nielsen KL, Sønderkær M, Iovene M, Torres GA, Jiang J, Veilleux RE, Bachem CW, de Boer J, Borm T, Kloosterman B, van Eck H, Datema E, Hekkert B, Goverse A, van Ham RC, Visser RG | display-authors = 6 | title = Genome sequence and analysis of the tuber crop potato | journal = Nature | volume = 475 | issue = 7355 | pages = 189–195 | date = July 2011 | pmid = 21743474 | doi = 10.1038/nature10158 | doi-access = free | hdl = 10533/238440 | hdl-access = free }}</ref>) and allopolyploids (such as canola, wheat and cotton) can be found among both wild and domesticated plant species.

Most polyploids display novel variation or morphologies relative to their parental species, that may contribute to the processes of [[speciation]] and eco-niche exploitation.<ref name="Rieseberg-2007" /><ref name="Comai-2005" /> The mechanisms leading to novel variation in newly formed allopolyploids may include gene dosage effects (resulting from more numerous copies of genome content), the reunion of divergent gene regulatory hierarchies, chromosomal rearrangements, and [[epigenetic]] remodeling, all of which affect gene content and/or expression levels.<ref name="Osborn-2003">{{cite journal | vauthors = Osborn TC, Pires JC, Birchler JA, Auger DL, Chen ZJ, Lee HS, Comai L, Madlung A, Doerge RW, Colot V, Martienssen RA | display-authors = 6 | title = Understanding mechanisms of novel gene expression in polyploids | journal = Trends in Genetics | volume = 19 | issue = 3 | pages = 141–147 | date = March 2003 | pmid = 12615008 | doi = 10.1016/S0168-9525(03)00015-5 }}</ref><ref name="Chen-2006">{{cite journal | vauthors = Chen ZJ, Ni Z | title = Mechanisms of genomic rearrangements and gene expression changes in plant polyploids | journal = BioEssays | volume = 28 | issue = 3 | pages = 240–252 | date = March 2006 | pmid = 16479580 | pmc = 1986666 | doi = 10.1002/bies.20374 }}</ref><ref name="Chen-2007">{{cite journal | vauthors = Chen ZJ | title = Genetic and epigenetic mechanisms for gene expression and phenotypic variation in plant polyploids | journal = Annual Review of Plant Biology | volume = 58 | pages = 377–406 | year = 2007 | issue = 1 | pmid = 17280525 | pmc = 1949485 | doi = 10.1146/annurev.arplant.58.032806.103835 | bibcode = 2007AnRPB..58..377C }}</ref><ref>{{cite journal | vauthors = Albertin W, Balliau T, Brabant P, Chèvre AM, Eber F, Malosse C, Thiellement H | title = Numerous and rapid nonstochastic modifications of gene products in newly synthesized Brassica napus allotetraploids | journal = Genetics | volume = 173 | issue = 2 | pages = 1101–1113 | date = June 2006 | pmid = 16624896 | pmc = 1526534 | doi = 10.1534/genetics.106.057554 }}</ref> Many of these rapid changes may contribute to reproductive isolation and speciation. However, seed generated from [[interploidy hybridization|interploidy crosses]], such as between polyploids and their parent species, usually have aberrant endosperm development which impairs their viability,<ref>{{cite journal | vauthors = Pennington PD, Costa LM, Gutierrez-Marcos JF, Greenland AJ, Dickinson HG | title = When genomes collide: aberrant seed development following maize interploidy crosses | journal = Annals of Botany | volume = 101 | issue = 6 | pages = 833–843 | date = April 2008 | pmid = 18276791 | pmc = 2710208 | doi = 10.1093/aob/mcn017 }}</ref><ref>{{cite journal | vauthors = von Wangenheim KH, Peterson HP | title = Aberrant endosperm development in interploidy crosses reveals a timer of differentiation | journal = Developmental Biology | volume = 270 | issue = 2 | pages = 277–289 | date = June 2004 | pmid = 15183714 | doi = 10.1016/j.ydbio.2004.03.014 | doi-access =  }}</ref> thus contributing to [[polyploid speciation]]. Polyploids may also interbreed with diploids and produce polyploid seeds, as observed in the agamic complexes of ''[[Crepis]]''.<ref>{{cite journal | vauthors = Whitton J, Sears CJ, Maddison WP | title = Co-occurrence of related asexual, but not sexual, lineages suggests that reproductive interference limits coexistence | journal = Proceedings. Biological Sciences | volume = 284 | issue = 1868 | article-number = 20171579 | date = December 2017 | pmid = 29212720 | pmc = 5740271 | doi = 10.1098/rspb.2017.1579 }}</ref>

Some plants are triploid. As [[meiosis]] is disturbed, these plants are sterile, with all plants having the same genetic constitution: Among them, the exclusively vegetatively propagated [[Crocus sativus|saffron crocus]] (''Crocus sativus''). Also, the extremely rare Tasmanian shrub ''[[Lomatia tasmanica]]'' is a triploid sterile species.

There are few naturally occurring polyploid [[conifers]].<ref>{{cite journal | vauthors = Halabi K, Shafir A, Mayrose I | title = PloiDB: The plant ploidy database | journal = The New Phytologist | date = June 2023 | volume = 240 | issue = 3 | pages = 918–927 | pmid = 37337836 | doi = 10.1111/nph.19057 | bibcode = 2023NewPh.240..918H | doi-access = free }}</ref> One example is the Coast Redwood ''[[Sequoia sempervirens]]'', which is a hexaploid (6''x'') with 66 chromosomes (2''n'' = 6''x'' = 66), although the origin is unclear.<ref>{{cite journal |id={{INIST|13965465}} | vauthors = Ahuja MR, Neale DB |title=Origins of Polyploidy in Coast Redwood (''Sequoia sempervirens'' (D. Don) Endl.) and Relationship of Coast Redwood to other Genera of Taxodiaceae |journal=Silvae Genetica |volume=51 |pages=2–3 |year=2002 }}</ref>

Aquatic plants, especially the [[Monocotyledon]]s, include a large number of polyploids.<ref>{{cite journal |doi=10.1016/0304-3770(93)90071-4 |title=Studies of hybridization and chromosome number variation in aquatic angiosperms: Evolutionary implications |year=1993 | vauthors = Les DH, Philbrick CT |journal=Aquatic Botany |volume=44 |issue=2–3 |pages=181–228|bibcode=1993AqBot..44..181L }}</ref>

==== Crops ====
The induction of polyploidy is a common technique to overcome the sterility of a hybrid species during plant breeding. For example, [[triticale]] is the hybrid of [[wheat]] (''Triticum turgidum'') and [[rye]] (''Secale cereale''). It combines sought-after characteristics of the parents, but the initial hybrids are sterile. After polyploidization, the hybrid becomes fertile and can thus be further propagated to become triticale.

In some situations, polyploid crops are preferred because they are sterile. For example, many seedless fruit varieties are seedless as a result of polyploidy. Such crops are propagated using asexual techniques, such as [[grafting]].

Polyploidy in crop plants is most commonly induced by treating seeds with the chemical [[Colchicine#Botanical use and seedless fruit|colchicine]].

===== Examples =====

* Triploid crops: some [[apple]] varieties (such as [[Belle de Boskoop]], [[Jonagold]], [[Mutsu (apple)|Mutsu]], [[Ribston Pippin]]), [[banana]], [[citrus]], [[ginger]], [[watermelon]],<ref>{{cite news |last1=Karp |first1=David |title=Seedless Fruits Make Others Needless |url=https://www.theledger.com/story/news/2007/03/25/seedless-fruits-make-others-needless/25840915007/ |work=The Ledger |agency=The New York Times |date=25 March 2007 }}</ref> [[Crocus sativus|saffron crocus]], white pulp of coconut
* Tetraploid crops: very few [[apple]] varieties, [[durum]] or [[macaroni]] [[wheat]], [[cotton]], [[potato]], [[canola]]/[[rapeseed]], [[leek]], [[tobacco]], [[peanut]], [[kinnow]], [[Pelargonium]]
* Hexaploid crops: [[chrysanthemum]], bread [[wheat]], [[triticale]], [[oat]], [[kiwifruit]]<ref name="Crowhurst-1992" />
* Octaploid crops: [[strawberry]], [[dahlia]], [[pansies]], [[sugar cane]], oca (''[[Oxalis tuberosa]]'')<ref>{{cite book| vauthors = Emshwiller E |year=2006 |title= Documenting Domestication: New Genetic and Archaeological Paradigms |chapter= Origins of polyploid crops: The example of the octaploid tuber crop ''Oxalis tuberosa'' |publisher=University of California Press |location=Berkeley, CA | veditors = Zeder MA, Decker-Walters D, Emshwiller E, Bradley D, Smith BD |isbn=978-0-520-24638-6 |pages=153–168 }}</ref>
* Dodecaploid crops: some [[sugar cane]] hybrids<ref>{{cite journal | vauthors = Le Cunff L, Garsmeur O, Raboin LM, Pauquet J, Telismart H, Selvi A, Grivet L, Philippe R, Begum D, Deu M, Costet L, Wing R, Glaszmann JC, D'Hont A | display-authors = 6 | title = Diploid/polyploid syntenic shuttle mapping and haplotype-specific chromosome walking toward a rust resistance gene (Bru1) in highly polyploid sugarcane (2n approximately 12x approximately 115) | journal = Genetics | volume = 180 | issue = 1 | pages = 649–660 | date = September 2008 | pmid = 18757946 | pmc = 2535714 | doi = 10.1534/genetics.108.091355 }}</ref>

Some crops are found in a variety of ploidies: [[tulip]]s and [[lily|lilies]] are commonly found as both diploid and triploid; [[daylilies]] (''Hemerocallis'' cultivars) are available as either diploid or tetraploid; apples and [[kinnow|kinnow mandarins]] can be diploid, triploid, or tetraploid.

=== Fungi ===

Besides plants and animals, the evolutionary history of various [[Fungus|fungal species]] is dotted by past and recent whole-genome duplication events (see Albertin and Marullo 2012<ref name="Albertin-2012">{{cite journal | vauthors = Albertin W, Marullo P | title = Polyploidy in fungi: evolution after whole-genome duplication | journal = Proceedings. Biological Sciences | volume = 279 | issue = 1738 | pages = 2497–2509 | date = July 2012 | pmid = 22492065 | pmc = 3350714 | doi = 10.1098/rspb.2012.0434 }}</ref> for review). Several examples of polyploids are known:
*autopolyploid: the aquatic fungi of genus ''Allomyces'',<ref>{{cite journal | vauthors = Emerson R, Wilson CM |year=1954 |title=Interspecific Hybrids and the Cytogenetics and Cytotaxonomy of Euallomyces |journal=Mycologia |volume=46 |issue=4 |pages=393–434 |jstor=4547843|doi=10.1080/00275514.1954.12024382 }}</ref> some ''[[Saccharomyces cerevisiae]]'' strains used in [[baker]]y,<ref>{{cite journal | vauthors = Albertin W, Marullo P, Aigle M, Bourgais A, Bely M, Dillmann C, DE Vienne D, Sicard D | display-authors = 6 | title = Evidence for autotetraploidy associated with reproductive isolation in Saccharomyces cerevisiae: towards a new domesticated species | journal = Journal of Evolutionary Biology | volume = 22 | issue = 11 | pages = 2157–2170 | date = November 2009 | pmid = 19765175 | doi = 10.1111/j.1420-9101.2009.01828.x | doi-access = free }}</ref> etc.
*allopolyploid: the widespread ''[[Cyathus stercoreus]]'',<ref>{{cite journal | vauthors = Lu BC |year=1964 |title=Polyploidy in the Basidiomycete ''Cyathus stercoreus'' |journal=American Journal of Botany |volume=51 |issue=3 |pages=343–347 |jstor=2440307 |doi=10.2307/2440307}}</ref> the allotetraploid lager yeast ''[[Saccharomyces pastorianus]]'',<ref>{{cite journal | vauthors = Libkind D, Hittinger CT, Valério E, Gonçalves C, Dover J, Johnston M, Gonçalves P, Sampaio JP | display-authors = 6 | title = Microbe domestication and the identification of the wild genetic stock of lager-brewing yeast | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 108 | issue = 35 | pages = 14539–14544 | date = August 2011 | pmid = 21873232 | pmc = 3167505 | doi = 10.1073/pnas.1105430108 | doi-access = free | bibcode = 2011PNAS..10814539L }}</ref> the allotriploid wine spoilage yeast ''[[Dekkera bruxellensis]]'',<ref>{{cite journal | vauthors = Borneman AR, Zeppel R, Chambers PJ, Curtin CD | title = Insights into the Dekkera bruxellensis genomic landscape: comparative genomics reveals variations in ploidy and nutrient utilisation potential amongst wine isolates | journal = PLOS Genetics | volume = 10 | issue = 2 | article-number = e1004161 | date = February 2014 | pmid = 24550744 | pmc = 3923673 | doi = 10.1371/journal.pgen.1004161 | doi-access = free }}</ref> etc.
*paleopolyploid: the human pathogen ''[[Rhizopus oryzae]]'',<ref>{{cite journal | vauthors = Ma LJ, Ibrahim AS, Skory C, Grabherr MG, Burger G, Butler M, Elias M, Idnurm A, Lang BF, Sone T, Abe A, Calvo SE, Corrochano LM, Engels R, Fu J, Hansberg W, Kim JM, Kodira CD, Koehrsen MJ, Liu B, Miranda-Saavedra D, O'Leary S, Ortiz-Castellanos L, Poulter R, Rodriguez-Romero J, Ruiz-Herrera J, Shen YQ, Zeng Q, Galagan J, Birren BW, Cuomo CA, Wickes BL | display-authors = 6 | title = Genomic analysis of the basal lineage fungus Rhizopus oryzae reveals a whole-genome duplication | journal = PLOS Genetics | volume = 5 | issue = 7 | article-number = e1000549 | date = July 2009 | pmid = 19578406 | pmc = 2699053 | doi = 10.1371/journal.pgen.1000549 | veditors = Madhani HD | doi-access = free }}</ref> the genus ''[[Saccharomyces]]'',<ref>{{cite journal | vauthors = Wong S, Butler G, Wolfe KH | title = Gene order evolution and paleopolyploidy in hemiascomycete yeasts | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 99 | issue = 14 | pages = 9272–9277 | date = July 2002 | pmid = 12093907 | pmc = 123130 | doi = 10.1073/pnas.142101099 | doi-access = free | bibcode = 2002PNAS...99.9272W | jstor = 3059188 }}</ref> etc.

In addition, polyploidy is frequently associated with [[Hybrid (biology)|hybridization]] and reticulate evolution that appear to be highly prevalent in several fungal taxa. Indeed, [[Hybrid speciation|homoploid speciation]] (hybrid speciation without a change in [[chromosome]] number) has been evidenced for some fungal species (such as the [[basidiomycota]] ''[[Microbotryum violaceum]]''<ref>{{cite journal | vauthors = Devier B, Aguileta G, Hood ME, Giraud T | title = Using phylogenies of pheromone receptor genes in the Microbotryum violaceum species complex to investigate possible speciation by hybridization | journal = Mycologia | volume = 102 | issue = 3 | pages = 689–696 | year = 2009 | pmid = 20524600 | doi = 10.3852/09-192 }}</ref>).

[[File:Polyploidy in fungi.png|thumb|left|upright=1.2|Schematic phylogeny of the Chromalveolata. Red circles indicate polyploidy, blue squares indicate hybridization. From Albertin and Marullo, 2012<ref name="Albertin-2012" />]]
As for plants and animals, fungal hybrids and polyploids display structural and functional modifications compared to their progenitors and diploid counterparts. In particular, the structural and functional outcomes of polyploid ''Saccharomyces'' genomes strikingly reflect the evolutionary fate of plant polyploid ones. Large chromosomal rearrangements<ref>{{cite journal | vauthors = Dunn B, Sherlock G | title = Reconstruction of the genome origins and evolution of the hybrid lager yeast Saccharomyces pastorianus | journal = Genome Research | volume = 18 | issue = 10 | pages = 1610–1623 | date = October 2008 | pmid = 18787083 | pmc = 2556262 | doi = 10.1101/gr.076075.108 }}</ref> leading to [[Chimera (genetics)|chimeric]] chromosomes<ref>{{cite journal | vauthors = Nakao Y, Kanamori T, Itoh T, Kodama Y, Rainieri S, Nakamura N, Shimonaga T, Hattori M, Ashikari T | display-authors = 6 | title = Genome sequence of the lager brewing yeast, an interspecies hybrid | journal = DNA Research | volume = 16 | issue = 2 | pages = 115–129 | date = April 2009 | pmid = 19261625 | pmc = 2673734 | doi = 10.1093/dnares/dsp003 }}</ref> have been described, as well as more punctual genetic modifications such as gene loss.<ref>{{cite journal | vauthors = Scannell DR, Byrne KP, Gordon JL, Wong S, Wolfe KH | title = Multiple rounds of speciation associated with reciprocal gene loss in polyploid yeasts | journal = Nature | volume = 440 | issue = 7082 | pages = 341–345 | date = March 2006 | pmid = 16541074 | doi = 10.1038/nature04562 | hdl-access = free | bibcode = 2006Natur.440..341S | hdl = 2262/22660 }}</ref> The homoealleles of the allotetraploid yeast ''S. pastorianus'' show unequal contribution to the [[transcriptome]].<ref>{{cite journal | vauthors = Minato T, Yoshida S, Ishiguro T, Shimada E, Mizutani S, Kobayashi O, Yoshimoto H | title = Expression profiling of the bottom fermenting yeast Saccharomyces pastorianus orthologous genes using oligonucleotide microarrays | journal = Yeast | volume = 26 | issue = 3 | pages = 147–165 | date = March 2009 | pmid = 19243081 | doi = 10.1002/yea.1654 }}</ref> [[Phenotypic]] diversification is also observed following polyploidization and/or hybridization in fungi,<ref>{{cite journal | vauthors = Lidzbarsky GA, Shkolnik T, Nevo E | title = Adaptive response to DNA-damaging agents in natural Saccharomyces cerevisiae populations from "Evolution Canyon", Mt. Carmel, Israel | journal = PLOS ONE | volume = 4 | issue = 6 | article-number = e5914 | date = June 2009 | pmid = 19526052 | pmc = 2690839 | doi = 10.1371/journal.pone.0005914 | veditors = Idnurm A | doi-access = free | bibcode = 2009PLoSO...4.5914L }}</ref> producing the fuel for [[natural selection]] and subsequent [[adaptation]] and speciation.

=== Chromalveolata ===
Other eukaryotic [[taxon|taxa]] have experienced one or more polyploidization events during their evolutionary history (see Albertin and Marullo, 2012<ref name="Albertin-2012" /> for review). The [[oomycetes]], which are non-true fungi members, contain several examples of paleopolyploid and polyploid species, such as within the genus ''[[Phytophthora]]''.<ref>{{cite journal | vauthors = Ioos R, Andrieux A, Marçais B, Frey P | title = Genetic characterization of the natural hybrid species Phytophthora alni as inferred from nuclear and mitochondrial DNA analyses | journal = Fungal Genetics and Biology | volume = 43 | issue = 7 | pages = 511–529 | date = July 2006 | pmid = 16626980 | doi = 10.1016/j.fgb.2006.02.006 | url = https://hal.archives-ouvertes.fr/hal-01136982/file/2006-FGB-Ioos%26al.pdf }}</ref> Some species of brown [[algae]] ([[Fucales]], Laminariales<ref>{{cite journal | vauthors = Phillips N, Kapraun DF, Gómez Garreta A, Ribera Siguan MA, Rull JL, Salvador Soler N, Lewis R, Kawai H | display-authors = 6 | title = Estimates of nuclear DNA content in 98 species of brown algae (Phaeophyta) | journal = AoB Plants | volume = 2011 | article-number = plr001 | year = 2011 | pmid = 22476472 | pmc = 3064507 | doi = 10.1093/aobpla/plr001 }}</ref> and [[diatoms]]<ref>{{cite journal |doi=10.1046/j.1529-8817.2002.t01-1-01233.x |title=Sexual Reproduction, Mating System, and Protoplast Dynamics of ''Seminavis'' (Bacillariophyceae) |year=2002 | vauthors = Chepurnov VA, Mann DG, Vyverman W, Sabbe K, Danielidis DB |journal=Journal of Phycology |volume=38 |issue=5 |pages=1004–1019|bibcode=2002JPcgy..38.1004C }}</ref>) contain apparent polyploid genomes. In the [[Alveolata]] group, the remarkable species ''[[Paramecium]] tetraurelia'' underwent three successive rounds of whole-genome duplication<ref>{{cite journal | vauthors = Aury JM, Jaillon O, Duret L, Noel B, Jubin C, Porcel BM, Ségurens B, Daubin V, Anthouard V, Aiach N, Arnaiz O, Billaut A, Beisson J, Blanc I, Bouhouche K, Câmara F, Duharcourt S, Guigo R, Gogendeau D, Katinka M, Keller AM, Kissmehl R, Klotz C, Koll F, Le Mouël A, Lepère G, Malinsky S, Nowacki M, Nowak JK, Plattner H, Poulain J, Ruiz F, Serrano V, Zagulski M, Dessen P, Bétermier M, Weissenbach J, Scarpelli C, Schächter V, Sperling L, Meyer E, Cohen J, Wincker P | display-authors = 6 | title = Global trends of whole-genome duplications revealed by the ciliate Paramecium tetraurelia | journal = Nature | volume = 444 | issue = 7116 | pages = 171–178 | date = November 2006 | pmid = 17086204 | doi = 10.1038/nature05230 | doi-access = free | bibcode = 2006Natur.444..171A }}</ref> and established itself as a major model for paleopolyploid studies.

=== Bacteria ===

Each ''[[Deinococcus radiodurans]]'' [[bacteria|bacterium]] contains 4-8 copies of its [[chromosome]].<ref name="Hansen-1978">{{cite journal | vauthors = Hansen MT | title = Multiplicity of genome equivalents in the radiation-resistant bacterium Micrococcus radiodurans | journal = Journal of Bacteriology | volume = 134 | issue = 1 | pages = 71–75 | date = April 1978 | pmid = 649572 | pmc = 222219 | doi = 10.1128/JB.134.1.71-75.1978 }}</ref> Exposure of ''D. radiodurans'' to [[X-ray]] irradiation or [[desiccation]] can shatter its [[genome]]s into hundred of short random fragments. Nevertheless, ''D. radiodurans'' is highly resistant to such exposures. The mechanism by which the genome is accurately restored involves RecA-mediated [[homologous recombination]] and a process referred to as extended [[synthesis-dependent strand annealing (SDSA)]].<ref name="Zahradka-2006">{{cite journal | vauthors = Zahradka K, Slade D, Bailone A, Sommer S, Averbeck D, Petranovic M, Lindner AB, Radman M | display-authors = 6 | title = Reassembly of shattered chromosomes in Deinococcus radiodurans | journal = Nature | volume = 443 | issue = 7111 | pages = 569–573 | date = October 2006 | pmid = 17006450 | doi = 10.1038/nature05160 | bibcode = 2006Natur.443..569Z }}</ref>

''[[Azotobacter vinelandii]]'' can contain up to 80 chromosome copies per cell.<ref name="Nagpal-1989">{{cite journal | vauthors = Nagpal P, Jafri S, Reddy MA, Das HK | title = Multiple chromosomes of Azotobacter vinelandii | journal = Journal of Bacteriology | volume = 171 | issue = 6 | pages = 3133–3138 | date = June 1989 | pmid = 2785985 | pmc = 210026 | doi = 10.1128/jb.171.6.3133-3138.1989 }}</ref> However this is only observed in fast growing cultures, whereas cultures grown in synthetic minimal media are not polyploid.<ref name="Maldonado-1994">{{cite journal | vauthors = Maldonado R, Jiménez J, Casadesús J | title = Changes of ploidy during the Azotobacter vinelandii growth cycle | journal = Journal of Bacteriology | volume = 176 | issue = 13 | pages = 3911–3919 | date = July 1994 | pmid = 8021173 | pmc = 205588 | doi = 10.1128/jb.176.13.3911-3919.1994 }}</ref>

===Archaea===

The [[archaea|archaeon]] ''[[Halobacterium salinarium]]'' is polyploid<ref name="Soppa-2011">{{cite journal | vauthors = Soppa J | title = Ploidy and gene conversion in Archaea | journal = Biochemical Society Transactions | volume = 39 | issue = 1 | pages = 150–154 | date = January 2011 | pmid = 21265763 | doi = 10.1042/BST0390150 }}</ref> and, like ''[[Deinococcus radiodurans]]'', is highly resistant to X-ray irradiation and desiccation, conditions that induce [[DNA]] double-strand breaks.<ref name="Kottemann-2005">{{cite journal | vauthors = Kottemann M, Kish A, Iloanusi C, Bjork S, DiRuggiero J | title = Physiological responses of the halophilic archaeon Halobacterium sp. strain NRC1 to desiccation and gamma irradiation | journal = Extremophiles | volume = 9 | issue = 3 | pages = 219–227 | date = June 2005 | pmid = 15844015 | doi = 10.1007/s00792-005-0437-4 | url = https://mnhn.hal.science/mnhn-02862359 }}</ref> Although chromosomes are shattered into many fragments, complete chromosomes can be regenerated by making use of overlapping fragments. The mechanism employs single-stranded [[DNA binding protein]] and is likely [[homologous recombination]]al repair.<ref name="DeVeaux-2007">{{cite journal | vauthors = DeVeaux LC, Müller JA, Smith J, Petrisko J, Wells DP, DasSarma S | title = Extremely radiation-resistant mutants of a halophilic archaeon with increased single-stranded DNA-binding protein (RPA) gene expression | journal = Radiation Research | volume = 168 | issue = 4 | pages = 507–514 | date = October 2007 | pmid = 17903038 | doi = 10.1667/RR0935.1 | bibcode = 2007RadR..168..507D | doi-access = free }}</ref>

== See also ==
* [[Diploidization]]
* [[Eukaryote hybrid genome]]
* [[Ploidy]]
* [[Polyploid complex]]
* [[Polysomy]]
* [[Reciprocal silencing]]
* [[Sympatry]]

== References ==
{{Reflist|30em}}

== Further reading ==
{{refbegin|30em}}
* {{cite book| vauthors = Snustad DP, Simmons MJ |year= 2006|title=Principles of Genetics|url=https://archive.org/details/principlesofgene04edsnus|url-access=registration|edition= 4th|publisher=John Wiley & Sons|location= Hoboken, New Jersey |isbn= 978-0-471-69939-2}}
* {{cite journal | vauthors = ((The ''Arabidopsis'' Genome Initiative)) | title = Analysis of the genome sequence of the flowering plant Arabidopsis thaliana | journal = Nature | volume = 408 | issue = 6814 | pages = 796–815 | date = December 2000 | pmid = 11130711 | doi = 10.1038/35048692 | doi-access = free | bibcode = 2000Natur.408..796T }}
* {{cite journal | vauthors = Eakin GS, Behringer RR | title = Tetraploid development in the mouse | journal = Developmental Dynamics | volume = 228 | issue = 4 | pages = 751–766 | date = December 2003 | pmid = 14648853 | doi = 10.1002/dvdy.10363 | doi-access = free }}
* {{cite journal | vauthors = Gaeta RT, Pires JC, Iniguez-Luy F, Leon E, Osborn TC | title = Genomic changes in resynthesized Brassica napus and their effect on gene expression and phenotype | journal = The Plant Cell | volume = 19 | issue = 11 | pages = 3403–3417 | date = November 2007 | pmid = 18024568 | pmc = 2174891 | doi = 10.1105/tpc.107.054346 | bibcode = 2007PlanC..19.3403G }}
* {{cite book |doi=10.1016/B978-012301463-4/50010-3 |chapter=Polyploidy in Animals |title=The Evolution of the Genome |date=2005 |last1=Gregory |first1=T. Ryan |last2=Mable |first2=Barbara K. |pages=427–517 |isbn=978-0-12-301463-4 }}
* {{cite journal | vauthors = Jaillon O, Aury JM, Brunet F, Petit JL, Stange-Thomann N, Mauceli E, Bouneau L, Fischer C, Ozouf-Costaz C, Bernot A, Nicaud S, Jaffe D, Fisher S, Lutfalla G, Dossat C, Segurens B, Dasilva C, Salanoubat M, Levy M, Boudet N, Castellano S, Anthouard V, Jubin C, Castelli V, Katinka M, Vacherie B, Biémont C, Skalli Z, Cattolico L, Poulain J, De Berardinis V, Cruaud C, Duprat S, Brottier P, Coutanceau JP, Gouzy J, Parra G, Lardier G, Chapple C, McKernan KJ, McEwan P, Bosak S, Kellis M, Volff JN, Guigó R, Zody MC, Mesirov J, Lindblad-Toh K, Birren B, Nusbaum C, Kahn D, Robinson-Rechavi M, Laudet V, Schachter V, Quétier F, Saurin W, Scarpelli C, Wincker P, Lander ES, Weissenbach J, Roest Crollius H | display-authors = 6 | title = Genome duplication in the teleost fish Tetraodon nigroviridis reveals the early vertebrate proto-karyotype | journal = Nature | volume = 431 | issue = 7011 | pages = 946–957 | date = October 2004 | pmid = 15496914 | doi = 10.1038/nature03025 | doi-access = free | bibcode = 2004Natur.431..946J }}
* {{cite journal | vauthors = Paterson AH, Bowers JE, Van de Peer Y, Vandepoele K | title = Ancient duplication of cereal genomes | journal = The New Phytologist | volume = 165 | issue = 3 | pages = 658–661 | date = March 2005 | pmid = 15720677 | doi = 10.1111/j.1469-8137.2005.01347.x | bibcode = 2005NewPh.165..658P | doi-access = free }}
* {{cite journal | vauthors = Raes J, Vandepoele K, Simillion C, Saeys Y, Van de Peer Y | title = Investigating ancient duplication events in the Arabidopsis genome | journal = Journal of Structural and Functional Genomics | volume = 3 | issue = 1–4 | pages = 117–129 | year = 2003 | pmid = 12836691 | doi = 10.1023/A:1022666020026 | doi-access = free }}
* {{cite journal | vauthors = Simillion C, Vandepoele K, Van Montagu MC, Zabeau M, Van de Peer Y | title = The hidden duplication past of Arabidopsis thaliana | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 99 | issue = 21 | pages = 13627–13632 | date = October 2002 | pmid = 12374856 | pmc = 129725 | doi = 10.1073/pnas.212522399 | doi-access = free | bibcode = 2002PNAS...9913627S | jstor = 3073458 }}
* {{cite journal | vauthors = Soltis DE, Soltis PS, Schemske DW, Hancock JF, Thompson JN, Husband BC, Judd WS |author-link2 = Pamela S. Soltis |year=2007 |title=Autopolyploidy in Angiosperms: Have We Grossly Underestimated the Number of Species? |journal=Taxon |volume=56 |issue=1 |pages=13–30 |jstor=25065732}}
* {{cite journal | vauthors = Soltis DE, Buggs RJ, Doyle JJ, Soltis PS |title=What we still don't know about polyploidy |journal=Taxon |volume=59 |issue=5 |pages=1387–1403 |year=2010 |doi=10.1002/tax.595006 |bibcode=2010Taxon..59.1387S }}
* {{cite journal | vauthors = Taylor JS, Braasch I, Frickey T, Meyer A, Van de Peer Y | title = Genome duplication, a trait shared by 22000 species of ray-finned fish | journal = Genome Research | volume = 13 | issue = 3 | pages = 382–390 | date = March 2003 | pmid = 12618368 | pmc = 430266 | doi = 10.1101/gr.640303 }}
* {{cite book |doi=10.1016/B978-012301463-4/50009-7 |chapter=Polyploidy in Plants |title=The Evolution of the Genome |date=2005 |last1=Tate |first1=Jennifer A. |last2=Soltis |first2=Douglas E. |last3=Soltis |first3=Pamela S. |pages=371–426 |isbn=978-0-12-301463-4 }}
* {{cite journal | vauthors = Van de Peer Y, Taylor JS, Meyer A | title = Are all fishes ancient polyploids? | journal = Journal of Structural and Functional Genomics | volume = 3 | issue = 1–4 | pages = 65–73 | year = 2003 | pmid = 12836686 | doi = 10.1023/A:1022652814749 | url = http://nbn-resolving.de/urn:nbn:de:bsz:352-opus-32682 }}
* {{cite journal | vauthors = Van de Peer Y | title = Tetraodon genome confirms Takifugu findings: most fish are ancient polyploids | journal = Genome Biology | volume = 5 | issue = 12 | page = 250 | year = 2004 | pmid = 15575976 | pmc = 545788 | doi = 10.1186/gb-2004-5-12-250 | doi-access = free }}
* {{cite book |doi=10.1016/B978-012301463-4/50008-5 |chapter=Large-Scale Gene and Ancient Genome Duplications |title=The Evolution of the Genome |date=2005 |last1=Van De Peer |first1=Yves |last2=Meyer |first2=Axel |pages=329–368 |isbn=978-0-12-301463-4 }}
* {{cite journal | vauthors = Wolfe KH, Shields DC | title = Molecular evidence for an ancient duplication of the entire yeast genome | journal = Nature | volume = 387 | issue = 6634 | pages = 708–713 | date = June 1997 | pmid = 9192896 | doi = 10.1038/42711 | doi-access = free | bibcode = 1997Natur.387..708W }}
* {{cite journal | vauthors = Wolfe KH | title = Yesterday's polyploids and the mystery of diploidization | journal = Nature Reviews. Genetics | volume = 2 | issue = 5 | pages = 333–341 | date = May 2001 | pmid = 11331899 | doi = 10.1038/35072009 }}
{{refend}}

== External links ==
{{wiktionary|mesopolyploid}}
{{wiktionary|neopolyploid}}
*[http://www.biology-pages.info/P/Polyploidy.html Polyploidy on Kimball's Biology Pages]
* [https://web.archive.org/web/20080908005054/http://www.polyploidy.org/ The polyploidy portal] a community-editable project with information, research, education, and a bibliography about polyploidy.
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[[Category:Classical genetics]]
[[Category:Speciation]]

[[he:פלואידיות#פוליפלואידיות]]
[[fi:Ploidia#Polyploidia]]
[[sv:Ploiditet#Polyploiditet]]