Polyploidy#Types

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{{anchor|Polyploid types}}

File:Organ-specific patterns of endopolyploidy in the giant ant Dinoponera australis - JHR-037-113-g001.jpg]]Polyploid types are labeled according to the number of chromosome sets in the nucleus. The letter x is used to represent the number of chromosomes in a single set:

• haploid (one set; 1x), for example male European fire ants
• diploid (two sets; 2x), for example humans
• triploid (three sets; 3x), for example sterile saffron crocus, or seedless watermelons, also common in the phylum Tardigrada{{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 }}
• tetraploid (four sets; 4x), for example, Plains viscacha rat, Salmonidae fish,{{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 }} the cotton Gossypium hirsutum{{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 }}
• pentaploid (five sets; 5x), for example Kenai Birch (Betula kenaica)
• hexaploid (six sets; 6x), for example some species of wheat,{{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 }} kiwifruit{{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 }}
• heptaploid or septaploid (seven sets; 7x), for example some cultured Siberian sturgeon{{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 }}
• octaploid or octoploid, (eight sets; 8x), for example Acipenser (genus of sturgeon fish), dahlias
• decaploid (ten sets; 10x), for example certain strawberries
• dodecaploid or duodecaploid (twelve sets; 12x), for example the plants Celosia argentea and Spartina anglica{{Hair space}}{{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 }} or the amphibian Xenopus ruwenzoriensis.
• tetratetracontaploid (forty-four sets; 44x), for example black mulberry

:{{ 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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:{{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 | pages = e0135411 | date = 2015 | pmid = 26266951 | doi = 10.1371/journal.pone.0135411 | pmc = 4534381 | bibcode = 2015PLoSO..1035411Z | doi-access = free }}

Autopolyploids are polyploids with multiple chromosome sets derived from a single taxon.

Two examples of natural autopolyploids are the piggyback plant, Tolmiea menzisii{{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}} and the white sturgeon, Acipenser transmontanum.{{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}} Most instances of autopolyploidy result from the fusion of unreduced (2n) gametes, which results in either triploid (n + 2n = 3n) or tetraploid (2n + 2n = 4n) offspring.{{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 | doi-access = free }} 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. Triploids may also persist through asexual reproduction. In fact, stable autotriploidy in plants is often associated with apomictic mating systems.{{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=}} In agricultural systems, autotriploidy can result in seedlessness, as in watermelons and bananas.{{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 }} Triploidy is also utilized in salmon and trout farming to induce sterility.{{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 }}{{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 }}

Rarely, autopolyploids arise from spontaneous, somatic genome doubling, which has been observed in apple (Malus domesticus) bud sports.{{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 }} This is also the most common pathway of artificially induced polyploidy, where methods such as protoplast fusion or treatment with colchicine, oryzalin or mitotic inhibitors are used to disrupt normal 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.{{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 }}

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 aneuploid gametes.{{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 }} 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{{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 }} and Arabidopsis lyrata,{{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 |pages=5218 |doi=10.1038/s41467-019-13159-5 |issn=2041-1723 |pmc=6861236 |pmid=31740675|bibcode=2019NatCo..10.5218M }} with specific adaptive alleles of these species shared between only the evolved polyploids.{{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 |pages=5218 |doi=10.1038/s41467-019-13159-5 |issn=2041-1723 |pmc=6861236 |pmid=31740675|bibcode=2019NatCo..10.5218M }}{{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 |pages=e1008900 |doi=10.1371/journal.pgen.1008900 |doi-access=free |issn=1553-7404 |pmc=7392332 |pmid=32667955}}

The high degree of homology among duplicated chromosomes causes autopolyploids to display polysomic inheritance.{{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 | doi-access = }} 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.{{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 | doi-access = }} 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.{{Cite book| vauthors = Stebbins GL |title=Types of polyploids; their classification and significance|year=1947|isbn=9780120176014|series=Advances in Genetics|volume=1|pages=403–429|language=en|doi=10.1016/s0065-2660(08)60490-3|pmid=20259289}}{{Cite book| vauthors = Stebbins GL |title=Variation and Evolution in Plants|publisher=Oxford University Press|year=1950}}{{page needed|date=March 2019}}

About half of all polyploids are thought to be the result of autopolyploidy,{{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 }}{{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 | doi-access = free }} although many factors make this proportion hard to estimate.{{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 | doi-access = free }}

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 (2n) gametes, which can take place before or after 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 hybrids produce unreduced gametes that fuse to form allopolyploid progeny.{{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 }} Hybridization followed by genome duplication may be a more common path to allopolyploidy because F₁ 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. In this case, allopolyploidy can actually restore normal, 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.

Because pairing between homoeologous chromosomes is rare in established allopolyploids, they may benefit from fixed heterozygosity of homoeologous alleles.{{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 }} In certain cases, such heterozygosity can have beneficial 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 Brassicaceous crops, the Triangle of U describes the relationships between the three common diploid Brassicas (B. oleracea, B. rapa, and B. nigra) and three allotetraploids (B. napus, B. juncea, and B. carinata) derived from hybridization among the diploid species. A similar relationship exists between three diploid species of Tragopogon (T. dubius, T. pratensis, and T. porrifolius) and two allotetraploid species (T. mirus and T. miscellus).{{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}} Complex patterns of allopolyploid evolution have also been observed in animals, as in the frog genus Xenopus.{{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 }}

{{main|Aneuploidy}}

Organisms in which a particular chromosome, or chromosome segment, is under- or over-represented are said to be 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.{{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}}

Polyploidy occurs in some tissues of animals that are otherwise diploid, such as human muscle tissues.{{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 }} 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.{{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 }} Hence ploidy is defined with respect to a cell.

{{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.

A polyploid that is newly formed.

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.

File:PaleopolyploidyTree.jpg 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 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 mutations 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.{{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 }}

In many cases, these events can be inferred only through comparing 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 evolutionary ancestor of the vertebrates (which includes the human lineage) and another near the origin of the teleost fishes. Angiosperms (flowering plants) have paleopolyploidy in their ancestry. All eukaryotes probably have experienced a polyploidy event at some point in their evolutionary history.

{{Main|Karyotype}}

A karyotype is the characteristic chromosome complement of a eukaryote species.{{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}}{{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}} The preparation and study of karyotypes is part of 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.

{{Main|Homoeology}}

Homoeologous chromosomes are those brought together following inter-species hybridization and allopolyploidization, and whose relationship was completely homologous in an ancestral species. For example, 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 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 in animals are more common in non-vertebrates{{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 }} such as flatworms, leeches, and brine shrimp. Within vertebrates, examples of stable polyploidy include the salmonids and many cyprinids (i.e. carp).{{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 }} Some fish have as many as 400 chromosomes. 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).{{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}} 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,{{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 }} "stealing" spermatophores 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 parenchymal liver cells, are polyploid,{{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 }}{{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 }} rare instances of polyploid mammals are known, but most often result in prenatal death. An 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'.{{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 }} 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.{{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 }} This rodent is not a rat, but kin to guinea pigs and chinchillas. Its "new" diploid (2n) number is 102 and so its cells are roughly twice normal size. Its closest living relation is Octomys mimax, the Andean Viscacha-Rat of the same family, whose 2n = 56. It was therefore surmised that an Octomys-like ancestor produced tetraploid (i.e., 2n = 4x = 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.{{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 }}{{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 }} Cold or heat shock has also been shown to result in unreduced amphibian gametes, though this occurs more commonly in eggs than in sperm.{{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 }} 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.{{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 }} 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 "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.

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

{{Further|Triploid syndrome}}

True polyploidy rarely occurs in humans, although polyploid cells occur in highly differentiated tissue, such as liver parenchyma, heart muscle, placenta and in bone marrow.{{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 | pages = e1007698 | date = October 2018 | pmid = 30312291 | pmc = 6200260 | doi = 10.1371/journal.pgen.1007698 | doi-access = free }}

{{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 }} Aneuploidy is more common.

Polyploidy occurs in humans in the form of 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.{{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}}

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.{{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 }} 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 miscarriages, while digyny predominates among triploid zygotes that survive into the fetal period.{{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 }} 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 phenotypes in triploid placentas and fetuses 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.{{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 }} In diandry, a partial hydatidiform mole develops. These parent-of-origin effects reflect the effects of 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.

A polyploidy event occurred within the stem lineage of the teleost fish.{{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 }}

File:Polyploidization.svg via polyploidy: A diploid cell undergoes failed meiosis, producing diploid gametes, 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.{{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 }}{{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 }}{{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 }}{{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 }} Huge explosions in angiosperm species diversity appear to have coincided with the timing of ancient genome duplications shared by many species.{{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 }} It has been established that 15% of angiosperm and 31% of fern speciation events are accompanied by ploidy increase.{{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 }}

Polyploid plants can arise spontaneously in nature by several mechanisms, including meiotic or mitotic failures, and fusion of unreduced (2n) gametes. Both autopolyploids (e.g. potato{{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 }}) 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. 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.{{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 }}{{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 }}{{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 | pmid = 17280525 | pmc = 1949485 | doi = 10.1146/annurev.arplant.58.032806.103835 }}{{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 }} Many of these rapid changes may contribute to reproductive isolation and speciation. However, seed generated from interploidy crosses, such as between polyploids and their parent species, usually have aberrant endosperm development which impairs their viability,{{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 }}{{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 = }} thus contributing to polyploid speciation. Polyploids may also interbreed with diploids and produce polyploid seeds, as observed in the agamic complexes of Crepis.{{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 | pages = 20171579 | date = December 2017 | pmid = 29212720 | pmc = 5740271 | doi = 10.1098/rspb.2017.1579 }}

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 saffron crocus (Crocus sativus). Also, the extremely rare Tasmanian shrub Lomatia tasmanica is a triploid sterile species.

There are few naturally occurring polyploid conifers.{{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 | doi-access = free }} One example is the Coast Redwood Sequoia sempervirens, which is a hexaploid (6x) with 66 chromosomes (2n = 6x = 66), although the origin is unclear.{{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 }}

Aquatic plants, especially the Monocotyledons, include a large number of polyploids.{{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 }}

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.

• Triploid crops: some apple varieties (such as Belle de Boskoop, Jonagold, Mutsu, Ribston Pippin), banana, citrus, ginger, watermelon,{{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 }} 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
• Octaploid crops: strawberry, dahlia, pansies, sugar cane, oca (Oxalis tuberosa){{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 }}
• Dodecaploid crops: some sugar cane hybrids{{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 }}

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

Besides plants and animals, the evolutionary history of various fungal species is dotted by past and recent whole-genome duplication events (see Albertin and Marullo 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 }} for review). Several examples of polyploids are known:

• autopolyploid: the aquatic fungi of genus Allomyces,{{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 }} some Saccharomyces cerevisiae strains used in bakery,{{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 }} etc.
• allopolyploid: the widespread Cyathus stercoreus,{{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}} the allotetraploid lager yeast Saccharomyces pastorianus,{{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 }} the allotriploid wine spoilage yeast Dekkera bruxellensis,{{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 | pages = e1004161 | date = February 2014 | pmid = 24550744 | pmc = 3923673 | doi = 10.1371/journal.pgen.1004161 | doi-access = free }} etc.
• paleopolyploid: the human pathogen Rhizopus oryzae,{{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 | pages = e1000549 | date = July 2009 | pmid = 19578406 | pmc = 2699053 | doi = 10.1371/journal.pgen.1000549 | veditors = Madhani HD | doi-access = free }} the genus Saccharomyces,{{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 }} etc.

In addition, polyploidy is frequently associated with hybridization and reticulate evolution that appear to be highly prevalent in several fungal taxa. Indeed, homoploid speciation (hybrid speciation without a change in chromosome number) has been evidenced for some fungal species (such as the basidiomycota Microbotryum violaceum{{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 }}).

File:Polyploidy in fungi.png

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{{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 }} leading to chimeric chromosomes{{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 }} have been described, as well as more punctual genetic modifications such as gene loss.{{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 }} The homoealleles of the allotetraploid yeast S. pastorianus show unequal contribution to the transcriptome.{{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 }} Phenotypic diversification is also observed following polyploidization and/or hybridization in fungi,{{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 | pages = e5914 | date = June 2009 | pmid = 19526052 | pmc = 2690839 | doi = 10.1371/journal.pone.0005914 | veditors = Idnurm A | doi-access = free | bibcode = 2009PLoSO...4.5914L }} producing the fuel for natural selection and subsequent adaptation and speciation.

Other eukaryotic taxa have experienced one or more polyploidization events during their evolutionary history (see Albertin and Marullo, 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.{{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 }} Some species of brown algae (Fucales, Laminariales{{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 | pages = plr001 | year = 2011 | pmid = 22476472 | pmc = 3064507 | doi = 10.1093/aobpla/plr001 }} and diatoms{{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 }}) contain apparent polyploid genomes. In the Alveolata group, the remarkable species Paramecium tetraurelia underwent three successive rounds of whole-genome duplication{{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 }} and established itself as a major model for paleopolyploid studies.

Each Deinococcus radiodurans bacterium contains 4-8 copies of its chromosome.{{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 }} Exposure of D. radiodurans to X-ray irradiation or desiccation can shatter its genomes 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).{{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 }}

Azotobacter vinelandii can contain up to 80 chromosome copies per cell.{{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 }} However this is only observed in fast growing cultures, whereas cultures grown in synthetic minimal media are not polyploid.{{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 }}

The archaeon Halobacterium salinarium is polyploid{{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 }} and, like Deinococcus radiodurans, is highly resistant to X-ray irradiation and desiccation, conditions that induce DNA double-strand breaks.{{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 }} 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 recombinational repair.{{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 }}

• Diploidization
• Eukaryote hybrid genome
• Ploidy
• Polyploid complex
• Polysomy
• Reciprocal silencing
• Sympatry

{{Reflist|30em}}

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{{refend}}

{{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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