Editing Polyploidy (section)

{{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>{{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 |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>{{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 }}</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 |pages=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>{{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 |issn=0028-646X|doi-access=free }}</ref>

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