Editing Polyploidy (section)

===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]]. Within vertebrates, examples of stable polyploidy include the [[salmonids]] and many [[cyprinids]] (i.e. [[carp]]).<ref name="Leggatt and Iwama">{{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> Some fish have as many as 400 chromosomes.<ref name="Leggatt and Iwama" /> 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="pmid17546077">{{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 }}</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 }}</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=Gurdon>{{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=Gurdon />

==== 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="Velicky2018">{{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 }}
</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="Ten Teachers">{{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="pmid23943708">{{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="Ten Teachers" /> 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.

==== 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>