Ploidia: diferenças entre revisões

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{{short description|Número de conjuntos de cromossomas presentes numa célula.}}
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[[File:Haploid vs diploid.svg|thumb|upright|Um conjunto haplóide que consiste num único grupo completo de cromossomas (igual ao conjunto monoplóide), conforme mostrado na figura acima, deve pertencer a uma espécie diplóide. Se um conjunto haplóide consiste em dois grupos, deve ser de uma espécie tetraplóide (quatro conjuntos).<ref name="Hartl2011">{{cite book|author=Daniel Hartl|title=Essential Genetics: A Genomics Perspective|year=2011|publisher=Jones & Bartlett Learning|isbn=978-0-7637-7364-9|pages=177|author-link=Daniel Hartl}}</ref>]]

'''Ploidia''' é o número de conjuntos completos de [[cromossoma]]s presentes numa [[célula]] e, em consequência, o número de [[alelo]]s possíveis para o conjunto de [[gene]]s [[Autossoma|autossómicos]] e [[Região pseudoautossómica|pseudo-autossómicos]] nela existentes. [[Célula somática|Células somáticas]], [[Tecido (biologia)|tecidos]] e [[Indivíduo#Biologia|organismos indivíduais]] podem ser descritos de acordo com o número de conjuntos de cromossomas presentes, o seu ''[[nível de ploidia]]'', como ''monoplóide'' (1 conjunto), ''diploide'' (2 conjuntos), ''triploide'' (3 conjuntos), ''tetraploide'' (4 conjuntos), ''pentaploide'' (5 conjuntos), e assim por diante.<ref name="U. R. Murty 1973 234–243">{{cite journal | title=Morphology of pachytene chromosomes and its bearing on the nature of polyploidy in the cytological races of Apluda mutica L. | author=U. R. Murty | journal=Genetica | year=1973 | volume=44 | issue=2 | pages=234–243 | doi=10.1007/bf00119108 | s2cid=45850598 }}</ref><ref name=Tateoka>{{cite journal |title=A contribution to the taxonomy of the ''Agrostis mertensii''-''flaccida'' complex (Poaceae) in Japan |author=Tuguo Tateoka |journal=Journal of Plant Research |date=May 1975 |volume=88 |issue=2 |pages=65–87 |doi=10.1007/bf02491243|s2cid=38029072 }}</ref> O termo genérico ''[[poliploidia|poliploide]]'' é frequentemente utilizado para descrever situações em que estejam presentes três ou mais conjuntos de cromossomas.<ref name=Rieger>{{Cite book | author1=Rieger, R. | author2=Michaelis, A. | author3=Green, M.M. | title=Glossary of Genetics and Cytogenetics: Classical and Molecular | edition=4th | publisher=Springer-Verlag | location=Berlin/Heidelberg | year=1976 | page=434 | isbn=978-3-540-07668-1 | doi=10.1007/978-3-642-96327-8| s2cid=10163081 }}</ref><ref name=Darlington>{{Cite book | author1=Darlington, C. D. (Cyril Dean) | title=Recent advances in cytology | publisher=P. Blakiston's son & co. | location=Philadelphia | year=1937 | page=60 | url=https://archive.org/details/recentadvancesin00darl}}</ref>
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==Descrição==

Cada [[espécie]] possui um número característico de [[cromossomo]]s, nos [[seres humanos]] esse conjunto esta representado em dose dupla (diploide). Mas existem algumas espécies que o conjunto básico de cromossomos está em múltiplas cópias ([[poliploide]]s). Porém, quando se considera a '''ploidia''', um conjunto básico de cromossomos é chamado [[haplóide]],como o caso de algumas bactérias ou leveduras, que têm fases haplóides da sua vida, (x), pois inclui apenas um cromossomo de cada tipo. A ploidia pode ser definida, portanto, como número de pares de cromossomos homólogos (cromossomos que têm informação para os mesmos genes e tem o mesmo tamanho) que cada célula apresenta.
Cada [[espécie]] possui um número característico de [[cromossomo]]s, nos [[seres humanos]] esse conjunto esta representado em dose dupla (diploide). Mas existem algumas espécies que o conjunto básico de cromossomos está em múltiplas cópias ([[poliploide]]s). Porém, quando se considera a '''ploidia''', um conjunto básico de cromossomos é chamado [[haplóide]],como o caso de algumas bactérias ou leveduras, que têm fases haplóides da sua vida, (x), pois inclui apenas um cromossomo de cada tipo. A ploidia pode ser definida, portanto, como número de pares de cromossomos homólogos (cromossomos que têm informação para os mesmos genes e tem o mesmo tamanho) que cada célula apresenta.
* 2 x um cromossomo = [[diploide]]
* 2 x um cromossomo = [[diploide]]
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Os gâmetas são produzidos por meiose de uma célula diplóide da linha germinativa. Durante a meiose, cromossomas semelhantes de origem materna e paterna (por exemplo o cromossoma 1 de origem materna com o cromossoma 1 de origem paterna) podem trocar pequenas partes de si próprios (crossing-over), e assim criar novos cromossomas que não foram herdados unicamente de um dos progenitores (podendo criar, por exemplo, um cromossoma 1 que apresenta regiões provenientes do cromossoma 1 de origem materna junto com outras regiões do cromossoma 1 de origem paterna). Quando um gâmeta masculino e um gâmeta feminino se unem (fertilização), forma-se um novo organismo diplóide.
Os gâmetas são produzidos por meiose de uma célula diplóide da linha germinativa. Durante a meiose, cromossomas semelhantes de origem materna e paterna (por exemplo o cromossoma 1 de origem materna com o cromossoma 1 de origem paterna) podem trocar pequenas partes de si próprios (crossing-over), e assim criar novos cromossomas que não foram herdados unicamente de um dos progenitores (podendo criar, por exemplo, um cromossoma 1 que apresenta regiões provenientes do cromossoma 1 de origem materna junto com outras regiões do cromossoma 1 de origem paterna). Quando um gâmeta masculino e um gâmeta feminino se unem (fertilização), forma-se um novo organismo diplóide.


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Virtually all [[sexual reproduction|sexually reproducing]] organisms are made up of somatic cells that are diploid or greater, but ploidy level may vary widely between different organisms, between different tissues within the same organism, and at different stages in an organism's life cycle. Half of all known plant genera contain polyploid species, and about two-thirds of all grasses are polyploid.<ref name="SnustadSimmons2012">{{cite book|author1=D. Peter Snustad|author2=Michael J. Simmons|title=Principles of Genetics, 6th edition|publisher=John Wiley & Sons|isbn=978-0-470-90359-9|page=115|year=2012}}</ref> Many animals are uniformly diploid, though polyploidy is common in invertebrates, reptiles, and amphibians. In some species, ploidy varies between individuals of the same species (as in the [[social insect]]s), and in others entire tissues and organ systems may be polyploid despite the rest of the body being diploid (as in the mammalian [[liver]]). For many organisms, especially plants and fungi, changes in ploidy level between generations are major drivers of [[speciation]]. In mammals and birds, ploidy changes are typically fatal.<ref name="Otto2007">{{cite journal|last1=Otto, Sarah P.|title=The Evolutionary Consequences of Polyploidy|journal=Cell|volume=131|issue=3|year=2007|pages=452–462|issn=0092-8674|doi=10.1016/j.cell.2007.10.022|pmid=17981114|s2cid=10054182|author1-link=Sarah Otto}}</ref> There is, however, evidence of polyploidy in organisms now considered to be diploid, suggesting that polyploidy has contributed to evolutionary diversification in plants and animals through successive rounds of polyploidization and rediploidization.<ref name="Mable2004">{{cite journal|last1=Mable|first1=B. K.|title='Why polyploidy is rarer in animals than in plants': myths and mechanisms|journal=Biological Journal of the Linnean Society|volume=82|issue=4|year=2004|pages=453–466|issn=0024-4066|doi=10.1111/j.1095-8312.2004.00332.x|doi-access=free}}</ref><ref name="Madlung2012">{{cite journal|last1=Madlung|first1=A|title=Polyploidy and its effect on evolutionary success: old questions revisited with new tools|journal=Heredity|volume=110|issue=2|year=2012|pages=99–104|issn=0018-067X|doi=10.1038/hdy.2012.79|pmid=23149459|pmc=3554449}}</ref>

Humans are diploid organisms, carrying two complete sets of chromosomes in their somatic cells: one set of 23 chromosomes from their father and one set of 23 chromosomes from their mother. The two sets combined provide a full complement of 46 chromosomes. This total number of individual chromosomes (counting all complete sets) is called the '''chromosome number'''. The number of chromosomes found in a single complete set of chromosomes is called the '''monoploid number''' (''x''). The '''haploid number''' (''n'') refers to the total number of chromosomes found in a [[gamete]] (a [[sperm]] or [[egg]] cell produced by [[meiosis]] in preparation for sexual reproduction). Under normal conditions, the haploid number is exactly half the total number of chromosomes present in the organism's somatic cells. For diploid organisms, the monoploid number and haploid number are equal; in humans, both are equal to 23. When a human [[germ cell]] undergoes meiosis, the diploid 46-chromosome complement is split in half to form haploid gametes. After fusion of a male and a female gamete (each containing 1 set of 23 chromosomes) during [[fertilization]], the resulting [[zygote]] again has the full complement of 46 chromosomes: 2 sets of 23 chromosomes.

==Etymology==

The term ''ploidy'' is a [[back-formation]] from ''haploidy'' and ''diploidy''. "Ploid" is a combination of Ancient Greek -πλόος (-plóos, “-fold”) and -ειδής (-''eidḗs''), from εἶδος (''eîdos'', "form, likeness").{{efn|Compare the etymology of [[tuple]], from the Latin for "-fold".}} The principal meaning of the [[Greek language|Greek]] word ᾰ̔πλόος (haplóos) is "single",<ref>{{cite web|url=http://www.perseus.tufts.edu/hopper/morph?l=(aploos&la=greek#lexicon|title=Greek Word Study Tool|website=www.perseus.tufts.edu}}</ref> from ἁ- (ha-, “one, same”).<ref>{{cite web|url=http://www.perseus.tufts.edu/hopper/morph?l=a(/ma&la=greek&can=a(/ma0&prior=a(plo/os|title=Greek Word Study Tool|website=www.perseus.tufts.edu}}</ref> διπλόος (''diplóos'') means "duplex" or "two-fold". Diploid therefore means "duplex-shaped" (compare "humanoid", "human-shaped").

Polish botanist [[Eduard Strasburger]] coined the terms ''haploid'' and ''diploid'' in 1905.{{efn|The original text in German is as follows: "Schließlich wäre es vielleicht erwünscht, wenn den Bezeichnungen Gametophyt und Sporophyt, die sich allein nur auf Pflanzen mit einfacher und mit doppelter Chromosomenzahl anwenden lassen, solche zur Seite gestellt würden, welche auch für das Tierreich passen. Ich erlaube mir zu diesem Zwecke die Worte Haploid und Diploid, bezw. haploidische und diploidische Generation vorzuschlagen."<ref>{{cite journal | last1=Strasburger | first1=Eduard | last2=Allen | first2=Charles E. | last3=Miyake | first3=Kilchi | last4=Overten | first4=James B. | date=1905 | title=Histologische Beiträge zur Vererbungsfrage | journal=Jahrbücher für Wissenschaftliche Botanik | volume=42 | pages=62 | url=https://archive.org/stream/jahrbcherfrwiss32stragoog | access-date=2017-03-11}}</ref><ref>{{cite book | last=Toepfer | first=Georg | date=2011 | title=Historisches Worterbüch der Biologie - Geschichte und Theorie der biologischen Grundbegriffe | location=Stuttgart | publisher=J.B. Metzler'sche Verlagsbuchhandlung und Carl Ernst Poeschel Verlag GmbH | page=169 | isbn=978-3-476-02317-9}}</ref>}} Some authors suggest that Strasburger based the terms on [[August Weismann]]'s conception of the id (or [[germ plasm]]),<ref>{{cite journal | author=Battaglia E | year=2009 | title=Caryoneme alternative to chromosome and a new caryological nomenclature | url=http://www.caryologia.unifi.it/past_volumes/62_4supplement/62-4_supplement.pdf | journal=Caryologia | volume=62 | issue=4 | pages=48}}</ref><ref>{{cite journal | author=David Haig | year=2008 | title=Homologous versus antithetic alternation of generations and the origin of sporophytes | url=http://dash.harvard.edu/bitstream/handle/1/11148775/Haig_HomologousVersus.pdf?sequence=3 | journal=The Botanical Review | volume=74 | issue=3 | pages=395–418 | doi=10.1007/s12229-008-9012-x| s2cid=207403936 | author-link=David Haig (biologist) }}</ref><ref>{{cite journal | last=Bennett | first=Michael D. | date=2004 | title=Biological relevance of polyploidy: ecology to genomics | journal=Biological Journal of the Linnean Society | volume=82 | issue=4 | pages=411–423 | doi=10.1111/j.1095-8312.2004.00328.x| doi-access=free }}</ref> hence haplo-''id'' and diplo-''id''. The two terms were brought into the English language from German through [[William Henry Lang]]'s 1908 translation of a 1906 textbook by Strasburger and colleagues.<ref>Strasburger, E.; Noll, F.; Schenck, H.; Karsten, G. 1908. ''A Textbook of botany'', 3rd English ed. (1908) [https://www.biodiversitylibrary.org/bibliography/1250#/summary], rev. with the 8th German ed. (1906) [http://nbn-resolving.de/urn:nbn:de:hbz:061:2-31697], translation by W. H. Lang of ''Lehrbuch der Botanik für Hochschulen''. Macmillan, London.</ref>{{Citation needed |date=January 2014}}

==Types of ploidy==

===Haploid and monoploid===
[[File:Difference of Haploid and Diploid Gene Regulation in Mendelian Genetics.svg|thumb|A comparison of [[sexual reproduction]] in predominantly haploid organisms and predominantly diploid organisms.<br/><br/>'''1)''' A haploid organism is on the left and a diploid organism is on the right.<br/>'''2 and 3)''' Haploid egg and sperm carrying the dominant purple gene and the recessive blue gene, respectively. These gametes are produced by simple mitosis of cells in the germ line.<br/>'''4 and 5)''' Diploid sperm and egg carrying the recessive blue gene and the dominant purple gene, respectively. These gametes are produced by meiosis, which halves the number of chromosomes in the diploid germ cells.<br/>'''6)''' The short-lived diploid state of haploid organisms, a zygote generated by the union of two haploid gametes during sex.<br/>'''7)''' The diploid zygote which has just been fertilized by the union of haploid egg and sperm during sex.<br/>'''8)''' Cells of the diploid structure quickly undergo meiosis to produce spores containing the meiotically halved number of chromosomes, restoring haploidy. These spores express either the mother's dominant gene or the father's recessive gene and proceed by mitotic division to build a new entirely haploid organism.<br/>'''9)''' The diploid zygote proceeds by mitotic division to build a new entirely diploid organism. These cells possess both the purple and blue genes, but only the purple gene is expressed since it is dominant over the recessive blue gene.]]

The term '''haploid''' is used with two distinct but related definitions. In the most generic sense, haploid refers to having the number of sets of chromosomes normally found in a [[gamete]].<ref>{{cite web |title=MGI Glossary |url=http://www.informatics.jax.org/glossary/haploid |website=Mouse Genome Informatics |publisher=The Jackson Laboratory |access-date=6 July 2019 |location=Bar Harbor, Maine}}</ref> Because two gametes necessarily combine during sexual reproduction to form a single zygote from which somatic cells are generated, healthy gametes always possess exactly half the number of sets of chromosomes found in the somatic cells, and therefore "haploid" in this sense refers to having exactly half the number of sets of chromosomes found in a somatic cell. By this definition, an organism whose gametic cells contain a single copy of each chromosome (one set of chromosomes) may be considered haploid while the somatic cells, containing two copies of each chromosome (two sets of chromosomes), are diploid. This scheme of diploid somatic cells and haploid gametes is widely used in the animal kingdom and is the simplest to illustrate in diagrams of genetics concepts. But this definition also allows for haploid gametes with ''more than one'' set of chromosomes. As given above, gametes are by definition haploid, regardless of the actual number of sets of chromosomes they contain. An organism whose somatic cells are tetraploid (four sets of chromosomes), for example, will produce gametes by meiosis that contain two sets of chromosomes. These gametes might still be called haploid even though they are numerically diploid.

An alternative usage defines "haploid" as having a single copy of each chromosome – that is, one and only one set of chromosomes.<ref>{{cite web |title=Talking Glossary of Genetic Terms |url=https://www.genome.gov/genetics-glossary/haploid |website=National Human Genome Research Institute |access-date=6 July 2019}}</ref> In this case, the nucleus of a [[eukaryote|eukaryotic]] cell is only said to be haploid if it has a single set of [[chromosome]]s, each one not being part of a pair. By extension a cell may be called haploid if its nucleus has one set of chromosomes, and an organism may be called haploid if its body cells (somatic cells) have one set of chromosomes per cell. By this definition haploid therefore would not be used to refer to the gametes produced by the tetraploid organism in the example above, since these gametes are numerically diploid. The term '''monoploid''' is often used as a less ambiguous way to describe a single set of chromosomes; by this second definition, haploid and monoploid are identical and can be used interchangeably.

[[Gamete]]s ([[sperm]] and [[egg cell|ova]]) are haploid cells. The haploid gametes produced by most organisms combine to form a [[zygote]] with ''n'' pairs of chromosomes, i.e. 2''n'' chromosomes in total. The chromosomes in each pair, one of which comes from the sperm and one from the egg, are said to be [[homologous chromosomes|homologous]]. Cells and organisms with pairs of homologous chromosomes are called diploid. For example, most animals are diploid and produce haploid gametes. During [[meiosis]], sex cell precursors have their number of chromosomes halved by randomly "choosing" one member of each pair of chromosomes, resulting in haploid gametes. Because homologous chromosomes usually differ genetically, gametes usually differ genetically from one another.{{citation needed |date=March 2017}}

All [[plant]]s and many [[fungus|fungi]] and [[alga]]e switch between a haploid and a diploid state, with one of the stages emphasized over the other. This is called [[alternation of generations]]. Most fungi and algae are haploid during the principal stage of their life cycle, as are some primitive plants like [[moss]]es. More recently evolved plants, like the gymnosperms and angiosperms, spend the majority of their life cycle in the diploid stage. Most animals are diploid, but male [[bees]], [[wasps]], and [[ants]] are haploid organisms because they develop from unfertilized, haploid eggs, while females (workers and queens) are diploid, making their system [[haplodiploid]].

In some cases there is evidence that the ''n'' chromosomes in a haploid set have resulted from duplications of an originally smaller set of chromosomes. This "base" number – the number of apparently originally unique chromosomes in a haploid set – is called the '''monoploid number''',<ref>Langlet, 1927.</ref> also known as '''basic''' or '''cardinal number''',<ref>Winge, 1917.</ref> or '''fundamental number'''.<ref>Manton, 1932.</ref><ref>{{cite journal | author = Fabbri F | year = 1963 | title = Primo supplemento alle tavole cromosomiche delle Pteridophyta di Alberto Chiarugi | url = https://books.google.com/books?id=2ZTzAAAAMAAJ&q=%22fundamental+number%22 | journal = Caryologia | volume = 16 | pages = 237–335 }}</ref> As an example, the chromosomes of [[common wheat]] are believed to be derived from three different ancestral species, each of which had 7 chromosomes in its haploid gametes. The monoploid number is thus 7 and the haploid number is 3&nbsp;×&nbsp;7&nbsp;= 21. In general ''n'' is a multiple of ''x''. The somatic cells in a wheat plant have six sets of 7 chromosomes: three sets from the egg and three sets from the sperm which fused to form the plant, giving a total of 42 chromosomes. As a formula, for wheat 2''n''&nbsp;= 6''x''&nbsp;= 42, so that the haploid number ''n'' is 21 and the monoploid number ''x'' is 7. The gametes of common wheat are considered to be haploid, since they contain half the genetic information of somatic cells, but they are not monoploid, as they still contain three complete sets of chromosomes (''n''&nbsp;=&nbsp;3''x'').<ref>http://mcb.berkeley.edu/courses/mcb142/lecture%20topics/Amacher/LECTURE_10_CHROM_F08.pdf</ref>

In the case of wheat, the origin of its haploid number of 21 chromosomes from three sets of 7 chromosomes can be demonstrated. In many other organisms, although the number of chromosomes may have originated in this way, this is no longer clear, and the monoploid number is regarded as the same as the haploid number. Thus in humans, ''x''&nbsp;=&nbsp;''n''&nbsp;=&nbsp;23.

=== Diploid ===

'''Diploid''' cells have two [[Homologous chromosome|homologous]] copies of each [[chromosome]], usually one from the [[mother]] and one from the [[father]]. All or nearly all mammals are diploid organisms. The suspected tetraploid (possessing four chromosome sets) plains viscacha rat (''[[Tympanoctomys barrerae]]'') and golden viscacha rat (''[[Pipanacoctomys aureus]]'')<ref name=Gallardo2006>{{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 | year=2006 | pmid=16580173 | doi=10.1016/j.ygeno.2006.02.010 | doi-access=free }}</ref> have been regarded as the only known exceptions (as of 2004).<ref>{{cite journal | author=Gallardo M. H. | year=2004 | title=Whole-genome duplications in South American desert rodents (Octodontidae) | journal=Biological Journal of the Linnean Society | volume=82 | issue= 4| pages=443–451 | doi=10.1111/j.1095-8312.2004.00331.x |display-authors=etal| doi-access=free }}</ref> However, some genetic studies have rejected any [[polyploid]]ism in mammals as unlikely, and suggest that amplification and dispersion of repetitive sequences best explain the large genome size of these two rodents.<ref name="Svartman 2005">{{cite journal |doi=10.1016/j.ygeno.2004.12.004 |title=Molecular cytogenetics discards polyploidy in mammals |year=2005 |last1=Svartman |first1=Marta |last2=Stone |first2=Gary |last3=Stanyon |first3=Roscoe |journal=Genomics |volume=85 |issue=4 |pages=425–430 |pmid=15780745}}</ref> All normal diploid individuals have some small fraction of cells that display [[polyploid]]y. [[Human genome|Human]] diploid cells have 46 chromosomes (the [[Somatic (biology)|somatic]] number, ''2n'') and human haploid [[gametes]] (egg and sperm) have 23 chromosomes (''n''). [[Retrovirus]]es that contain two copies of their RNA genome in each viral particle are also said to be diploid. Examples include [[human foamy virus]], [[human T-lymphotropic virus]], and [[HIV]].<ref>{{Cite web |url=http://web.uct.ac.za/depts/mmi/jmoodie/hiv2.html |title=Archived copy |access-date=2008-05-14 |archive-url=https://archive.is/20030330094545/http://web.uct.ac.za/depts/mmi/jmoodie/hiv2.html |archive-date=2003-03-30 |url-status=dead }}</ref>

=== Polyploidy ===
{{main |Polyploidy}}

'''Polyploidy''' is the state where all cells have multiple sets of chromosomes beyond the basic set, usually 3 or more. Specific terms are '''triploid''' (3 sets), '''tetraploid''' (4 sets), pentaploid (5 sets), hexaploid (6 sets), heptaploid<ref name="U. R. Murty 1973 234–243"/> or septaploid<ref name="Tateoka"/> (7 sets), octoploid (8 sets), nonaploid (9 sets), decaploid (10 sets), undecaploid (11 sets), dodecaploid (12 sets), tridecaploid (13 sets), tetradecaploid (14 sets), etc.<ref name=Dierschke>{{cite journal |vauthors=Dierschke T, Mandáková T, Lysak MA, Mummenhoff K | 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 | date=September 2009 | pmid=19589857 | pmc=2729636 | doi=10.1093/aob/mcp161 }}</ref><ref name=Renny-Byfield>{{cite journal |url=http://aob.oxfordjournals.org/content/105/4/527.abstract |title=Flow cytometry and GISH reveal mixed ploidy populations and Spartina nonaploids with genomes of ''S. alterniflora'' and ''S. maritima'' origin |author=Simon Renny-Byfield |journal=Annals of Botany |year=2010 |volume=105 |issue=4 |pages=527–533 |doi=10.1093/aob/mcq008 |display-authors=etal |pmid=20150197 |pmc=2850792}}</ref><ref name=Hummer>{{cite journal |url=http://www.amjbot.org/content/96/3/713.full |title=Decaploidy in ''Fragaria iturupensis'' (Rosaceae) |author=Kim E. Hummer |journal=Am. J. Bot. |date=March 2009 |volume=96 |number=3 |pages=713–716 |doi=10.3732/ajb.0800285 |pmid=21628226 |display-authors=etal}}</ref><ref name=Talyshinski~>{{cite journal |url=http://www.cabdirect.org/abstracts/19911699005.html |title=Study of the fractional composition of the proteins in the compound fruit of polyploid mulberry |author=Talyshinskiĭ, G. M. |journal=Shelk |year=1990 |number=5 |pages=8–10}}</ref> Some higher ploidies include hexadecaploid (16 sets), dotriacontaploid (32 sets), and tetrahexacontaploid (64 sets),<ref>{{cite journal |url=https://www.jstage.jst.go.jp/article/csf/26/5/26_5_263/_pdf |title=Temperature dependence in Proliferation of tetraploid Meth-A cells in comparison with the parent diploid cells |author=Fujikawa-Yamamoto K |journal=Cell Structure and Function |volume=26 |issue=5 |pages=263–269 |year=2001 |doi=10.1247/csf.26.263|pmid=11831358 |doi-access=free }}</ref> though Greek terminology may be set aside for readability in cases of higher ploidy (such as "16-ploid").<ref name=Hummer /> [[Polytene chromosomes]] of plants and fruit flies can be 1024-ploid.<ref>{{cite book |url=https://books.google.com/books?id=Nrjn1kzN0_0C&pg=PA68 |title=Plant Chromosomes: Laboratory Methods |author1=Kiichi Fukui |author2=Shigeki Nakayama |isbn=9780849389191 |date=1996 }}</ref><ref>{{cite web |url=http://cricket.bio.indiana.edu/allied-data/lk/interactive-fly/aimorph/puffing.htm |title=Genes involved in tissue and organ development: Polytene chromosomes, endoreduplication and puffing |publisher=The Interactive Fly |access-date=2012-12-16 |archive-url=https://web.archive.org/web/20050504235437/http://cricket.bio.indiana.edu/allied-data/lk/interactive-fly/aimorph/puffing.htm |archive-date=2005-05-04 |url-status=dead }}</ref> Ploidy of systems such as the [[salivary gland]], [[elaiosome]], [[endosperm]], and [[trophoblast]] can exceed this, up to 1048576-ploid in the silk glands of the commercial silkworm ''[[Bombyx mori]]''.<ref name=D~Amato />

The chromosome sets may be from the same species or from closely related species. In the latter case, these are known as allopolyploids (or amphidiploids, which are allopolyploids that behave as if they were normal diploids). Allopolyploids are formed from the hybridization of two separate species. In plants, this probably most often occurs from the pairing of meiotically unreduced [[gametes]], and not by diploid–diploid hybridization followed by chromosome doubling.<ref>{{cite journal | last1=Ramsey | first1=J. | last2=Schemske | first2=D. W. | title=Neopolyploidy in Flowering Plants | journal=Annual Review of Ecology and Systematics | volume=33 | pages=589–639 | year=2002 | doi=10.1146/annurev.ecolsys.33.010802.150437 | url=http://www.plantbiology.msu.edu/files/RAMSEY%20AND%20SCHEMSKE%202002%289%29.pdf | access-date=2015-02-07 | archive-url=https://web.archive.org/web/20120319000622/http://www.plantbiology.msu.edu/files/RAMSEY%20AND%20SCHEMSKE%202002(9).pdf | archive-date=2012-03-19 | url-status=dead }}</ref> The so-called [[Triangle of U|''Brassica'' triangle]] is an example of allopolyploidy, where three different parent species have hybridized in all possible pair combinations to produce three new species.

Polyploidy occurs commonly in plants, but rarely in animals. Even in diploid organisms, many [[somatic cell]]s are polyploid due to a process called [[endoreduplication]], where duplication of the [[genome]] occurs without [[mitosis]] (cell division). The extreme in polyploidy occurs in the [[fern]] genus ''[[Ophioglossum]]'', the adder's-tongues, in which polyploidy results in chromosome counts in the hundreds, or, in at least one case, well over one thousand.

It is possible for polyploid organisms to revert to lower ploidy by [[haploidisation]].

====In bacteria and archaea====

[[Polyploid]]y is a characteristic of the bacterium ''[[Deinococcus radiodurans]]'' <ref name="pmid649572">{{cite journal |vauthors=Hansen MT |title=Multiplicity of genome equivalents in the radiation-resistant bacterium Micrococcus radiodurans |journal=J. Bacteriol. |volume=134 |issue=1 |pages=71–75 |year=1978 |pmid=649572 |pmc=222219 |doi= 10.1128/JB.134.1.71-75.1978}}</ref> and of the [[archaea|archaeon]] ''[[Halobacterium salinarum]]''.<ref name="pmid21265763">{{cite journal |vauthors=Soppa J |title=Ploidy and gene conversion in Archaea |journal=Biochem. Soc. Trans. |volume=39 |issue=1 |pages=150–154 |year=2011 |pmid=21265763 |doi=10.1042/BST0390150 |s2cid=31385928 |url=https://semanticscholar.org/paper/db54f1b81e6138c1bcbb53f75e45f73dc740d611}}</ref> These two species are highly resistant to [[ionizing radiation]] and [[desiccation]], conditions that induce [[DNA]] double-strand breaks.<ref name="pmid17006450">{{cite journal |vauthors=Zahradka K, Slade D, Bailone A, Sommer S, Averbeck D, Petranovic M, Lindner AB, Radman M |title=Reassembly of shattered chromosomes in Deinococcus radiodurans |journal=Nature |volume=443 |issue=7111 |pages=569–573 |year=2006 |pmid=17006450 |doi=10.1038/nature05160 |bibcode=2006Natur.443..569Z |s2cid=4412830 }}</ref><ref name="pmid15844015">{{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 |year=2005 |pmid=15844015 |doi=10.1007/s00792-005-0437-4 |s2cid=8391234 }}</ref> This resistance appears to be due to efficient [[homologous recombination]]al repair.

===Variable or indefinite ploidy===

Depending on growth conditions, [[prokaryote]]s such as [[bacteria]] may have a chromosome copy number of 1 to 4, and that number is commonly fractional, counting portions of the chromosome partly replicated at a given time. This is because under exponential growth conditions the cells are able to replicate their DNA faster than they can divide.

In ciliates, the macronucleus is called '''ampliploid''', because only part of the genome is amplified.<ref>Schaechter, M. ''[https://books.google.com/books?id=DJLIhDnqMk0C&lpg=PP1&hl=pt-BR&pg=PA217#v=onepage&q&f=false Eukaryotic microbes]''. Amsterdam, Academic Press, 2012, p. 217.</ref>

===Mixoploidy===

Mixoploidy is the case where two cell lines, one diploid and one polyploid, [[Chimera (genetics)|coexist within the same organism]]. Though polyploidy in humans is not viable, mixoploidy has been found in live adults and children.<ref>{{cite journal |title=Mixoploidy in humans: two surviving cases of diploid-tetraploid mixoploidy and comparison with diploid-triploid mixoploidy. |author=Edwards MJ |display-authors=etal |pmid=7810564 |doi=10.1002/ajmg.1320520314 |volume=52 |issue=3 |journal=Am J Med Genet |pages=324–330|year=1994 }}</ref> There are two types: diploid-triploid mixoploidy, in which some cells have 46 chromosomes and some have 69,<ref>{{cite journal |title=46,XX/69,XXX diploid-triploid mixoploidy with hypothyroidism and precocious puberty. |last1=Järvelä |first1=IE |last2=Salo |first2=MK |last3=Santavuori |first3=P |last4=Salonen |first4=RK |pmid=8301657 |volume=30 |issue=11 |pmc=1016611 |journal=J Med Genet |pages=966–967 |doi=10.1136/jmg.30.11.966|year=1993 }}</ref> and diploid-tetraploid mixoploidy, in which some cells have 46 and some have 92 chromosomes. It is a major topic of cytology.

===Dihaploidy and polyhaploidy===

{{distinguish |text=[[Haplodiploid sex-determination system|haplodiploidy]] (where diploid and haploid individuals are different sexes)}}
Dihaploid and polyhaploid cells are formed by [[haploidisation]] of polyploids, i.e., by halving the chromosome constitution.

Dihaploids (which are diploid) are important for selective breeding of tetraploid crop plants (notably potatoes), because selection is faster with diploids than with tetraploids. Tetraploids can be reconstituted from the diploids, for example by somatic fusion.

The term "dihaploid" was coined by Bender<ref>{{cite journal | author=Bender K | year=1963 | title=Über die Erzeugung und Entstehung dihaploider Pflanzen bei ''Solanum tuberosum''". | journal=Zeitschrift für Pflanzenzüchtung | volume=50 | pages=141–166 }}</ref> to combine in one word the number of genome copies (diploid) and their origin (haploid). The term is well established in this original sense,<ref>Nogler, G.A. 1984. Gametophytic apomixis. In ''Embryology of angiosperms''. Edited by B.M. Johri. Springer, Berlin, Germany. pp. 475–518.</ref><ref>* {{cite journal | author=Pehu E | year=1996 | title=The current status of knowledge on the cellular biology of potato | journal=Potato Research | volume=39 | issue= 3| pages=429–435 | doi=10.1007/bf02357948| s2cid=32122774 }}</ref> but it has also been used for doubled monoploids or [[doubled haploidy|doubled haploids]], which are homozygous and used for genetic research.<ref>* {{cite journal |author1=Sprague G.F. |author2=Russell W.A. |author3=Penny L.H. | year=1960 | title=Mutations affecting quantitative traits in the selfed progeny of double monoploid maize stocks | journal=Genetics | volume=45 | issue=7 | pages=855–866 |pmid=17247970 |pmc=1210096 }}</ref>

===Euploidy and aneuploidy===

'''Euploidy''' ([[Ancient Greek|Greek]] ''eu'', "true" or "even") is the state of a cell or organism having one or more than one set of the same set of chromosomes, possibly excluding the [[sex chromosome|sex-determining chromosomes]]. For example, most human cells have 2 of each of the 23 homologous monoploid chromosomes, for a total of 46 chromosomes. A human cell with one extra set of the 23 normal chromosomes (functionally triploid) would be considered euploid. Euploid [[karyotype]]s would consequentially be a multiple of the [[Ploidy#Haploid and monoploid|haploid number]], which in humans is 23.

'''[[Aneuploidy]]''' is the state where one or more individual chromosomes of a normal set are absent or present in more than their usual number of copies (excluding the absence or presence of complete sets, which is considered euploidy). Unlike euploidy, aneuploid karyotypes will not be a multiple of the haploid number. In humans, examples of aneuploidy include having a single extra chromosome (as in [[Down syndrome]], where affected individuals have three copies of chromosome 21) or missing a chromosome (as in [[Turner syndrome]], where affected individuals are missing an X chromosome). Aneuploid [[karyotype]]s are given names with the suffix ''-somy'' (rather than ''-ploidy'', used for euploid karyotypes), such as [[trisomy]] and [[monosomy]].

===Homoploid===

Homoploid means "at the same ploidy level", i.e. having the same number of [[homologous chromosome]]s. For example, homoploid [[Hybrid (biology)|hybridization]] is hybridization where the offspring have the same ploidy level as the two parental species. This contrasts with a common situation in plants where chromosome doubling accompanies or occurs soon after hybridization. Similarly, homoploid speciation contrasts with [[polyploid speciation]].{{citation needed |date=March 2017}}

===Zygoidy and azygoidy===

Zygoidy is the state in which the chromosomes are paired and can undergo meiosis. The zygoid state of a species may be diploid or polyploid.<ref>{{cite book |publisher=Academic Press |isbn=978-0-12-017603-8 |last=Books |first=Elsevier Science & Technology |title=Advances in Genetics |date=1950}}</ref><ref name=Cosin2011>Cosín, Darío J. Díaz, Marta Novo, and Rosa Fernández. "[https://link.springer.com/chapter/10.1007%2F978-3-642-14636-7_5 Reproduction of Earthworms: Sexual Selection and Parthenogenesis.]" In Biology of Earthworms, edited by Ayten Karaca, 24:69–86. Berlin, Heidelberg: Springer Berlin Heidelberg, 2011.</ref> In the azygoid state the chromosomes are unpaired. It may be the natural state of some asexual species or may occur after meiosis. In diploid organisms the azygoid state is monoploid. (See below for dihaploidy.)

==Special cases==

===More than one nucleus per cell===

In the strictest sense, ploidy refers to the number of sets of chromosomes in a single [[nucleus (cell)|nucleus]] rather than in the cell as a whole. Because in most situations there is only one nucleus per cell, it is commonplace to speak of the ploidy of a cell, but in cases in which there is more than one nucleus per cell, more specific definitions are required when ploidy is discussed. Authors may at times report the total combined ploidy of all nuclei present within the cell membrane of a [[syncytium]],<ref name="D~Amato">Encyclopedia of the Life Sciences (2002) "Polyploidy" Francesco D'Amato and Mauro Durante</ref> though usually the ploidy of each nucleus is described individually. For example, a fungal [[dikaryon]] with two separate haploid nuclei is distinguished from a diploid cell in which the chromosomes share a nucleus and can be shuffled together.<ref>{{cite web |url=http://www.utm.utoronto.ca/~anders38/ms.pdf |title=Dikaryons, diploids, and evolution |author1=James B. Anderson |author2=Linda M Kohn |publisher=University of Toronto |access-date=2012-12-16 |archive-url=https://web.archive.org/web/20130527004555/http://www.utm.utoronto.ca/~anders38/ms.pdf |archive-date=2013-05-27 |url-status=dead }}</ref>

===Ancestral ploidy levels===

It is possible on rare occasions for ploidy to increase in the [[germline]], which can result in [[polyploid]] offspring and ultimately polyploid species. This is an important evolutionary mechanism in both plants and animals and is known as a primary driver of [[speciation]].<ref name="Mable2004"/> As a result, it may become desirable to distinguish between the ploidy of a species or variety as it presently breeds and that of an ancestor. The number of chromosomes in the ancestral (non-homologous) set is called the '''monoploid number''' (''x''), and is distinct from the haploid number (''n'') in the organism as it now reproduces.

[[Common wheat]] (''Triticum aestivum'') is an organism in which ''x'' and ''n'' differ. Each plant has a total of six sets of chromosomes (with two sets likely having been obtained from each of three different diploid species that are its distant ancestors). The somatic cells are hexaploid, 2''n''&nbsp;=&nbsp;6''x''&nbsp;=&nbsp;42 (where the monoploid number ''x''&nbsp;=&nbsp;7 and the haploid number ''n''&nbsp;=&nbsp;21). The gametes are haploid for their own species, but triploid, with three sets of chromosomes, by comparison to a probable evolutionary ancestor, [[einkorn wheat]].{{citation needed |date=March 2017}}

[[Tetraploidy]] (four sets of chromosomes, 2''n''&nbsp;=&nbsp;4''x'') is common in many [[plant]] species, and also occurs in [[amphibian]]s, [[reptile]]s, and [[insect]]s. For example, species of ''[[Xenopus]]'' (African toads) form a '''ploidy series''', featuring diploid (''[[Western clawed frog|X. tropicalis]]'', 2n=20), tetraploid (''[[African clawed frog|X. laevis]]'', 4n=36), octaploid (''[[De Witte's clawed frog|X. wittei]]'', 8n=72), and dodecaploid (''[[Uganda clawed frog|X. ruwenzoriensis]]'', 12n=108) species.<ref>{{cite journal |last1=Schmid |first1=M |last2=Evans |first2=BJ |last3=Bogart |first3=JP |title=Polyploidy in Amphibia |journal=Cytogenet. Genome Res. |date=2015 |volume=145 |issue=3–4 |pages=315–330 |doi=10.1159/000431388 |pmid=26112701|doi-access=free }}</ref>

Over evolutionary time scales in which [[chromosomal polymorphism]]s accumulate, these changes become less apparent by [[karyotype]] – for example, humans are generally regarded as diploid, but the [[2R hypothesis]] has confirmed two rounds of whole genome duplication in early vertebrate ancestors.

===Haplodiploidy===

Ploidy can also vary between individuals of the same species or at different stages of the [[biological life cycle|life cycle]].<ref>{{cite journal |vauthors=Parfrey LW, Lahr DJ, Katz LA | year=2008 | title=The dynamic nature of eukaryotic genomes | url=http://mbe.oxfordjournals.org/content/25/4/787.full | journal=Mol Biol Evol | volume=25 | issue= 4| pages=787–794 | doi=10.1093/molbev/msn032 | pmid=18258610 | pmc=2933061}}</ref><ref>{{cite journal | author=Qiu Y.-L., Taylor A. B., McManus H. A. | year=2012 | title=Evolution of the life cycle in land plants | journal=Journal of Systematics and Evolution | volume=50 | issue= 3| pages=171–194 | doi=10.1111/j.1759-6831.2012.00188.x| url=https://deepblue.lib.umich.edu/bitstream/2027.42/92043/1/j.1759-6831.2012.00188.x.pdf | hdl=2027.42/92043 | s2cid=40564254 }}</ref> In some insects it differs by [[eusociality|caste]]. In humans, only the gametes are haploid, but in many of the [[social insect]]s, including [[ant]]s, [[bee]]s, and [[termite]]s, certain individuals develop from unfertilized eggs, making them haploid for their entire lives, even as adults. In the Australian bulldog ant, ''[[Myrmecia pilosula]]'', a [[haplodiploid]] species, haploid individuals of this species have a single chromosome and diploid individuals have two chromosomes.<ref>{{cite journal |vauthors=Crosland MW, Crozier RH | title=Myrmecia pilosula, an Ant with Only One Pair of Chromosomes | journal=Science | volume=231 | issue=4743 | pages=1278 | year=1986 | pmid=17839565 | doi=10.1126/science.231.4743.1278 | bibcode=1986Sci...231.1278C | s2cid=25465053 }}</ref> In ''[[Entamoeba]]'', the ploidy level varies from 4''n'' to 40''n'' in a single population.<ref>{{cite web |url=https://bcrc.bio.umass.edu/courses/fall2010/biol/biolh100-03/sites/default/files/vazquez_eukaryotic_diversity_2010.pdf |title=Archived copy |access-date=2014-02-18 |url-status=dead |archive-url=https://web.archive.org/web/20140223015031/https://bcrc.bio.umass.edu/courses/fall2010/biol/biolh100-03/sites/default/files/vazquez_eukaryotic_diversity_2010.pdf |archive-date=2014-02-23 }}</ref> [[Alternation of generations]] occurs in most plants, with individuals "alternating" ploidy level between different stages of their sexual life cycle.

===Tissue-specific polyploidy===

In large multicellular organisms, variations in ploidy level between different tissues, organs, or cell lineages are common. Because the chromosome number is generally reduced only by the specialized process of meiosis, the somatic cells of the body inherit and maintain the chromosome number of the zygote by mitosis. However, in many situations somatic cells double their copy number by means of [[endoreduplication]] as an aspect of [[cellular differentiation]]. For example, the hearts of two-year-old human children contain 85% diploid and 15% tetraploid nuclei, but by 12 years of age the proportions become approximately equal, and adults examined contained 27% diploid, 71% tetraploid and 2% octaploid nuclei.<ref>{{cite book |url=https://books.google.com/books?id=VhLOSt1bq-wC&pg=PA234 |title=The Development and Regenerative Potential of Cardiac Muscle |author1=John O. Oberpriller |author2=A Mauro |publisher=Taylor&Francis|isbn=9783718605187 |year=1991 }}</ref>

== Adaptive and ecological significance of variation in ploidy ==

There is continued study and debate regarding the fitness advantages or disadvantages conferred by different ploidy levels. A study comparing the [[karyotypes]] of endangered or invasive plants with those of their relatives found that being polyploid as opposed to diploid is associated with a 14% lower risk of being endangered, and a 20% greater chance of being invasive.<ref name="Pandit">{{Cite journal | last=Pandit | first=M. K. |author2=Pocock, M. J. O. |author3=Kunin, W. E. | title=Ploidy influences rarity and invasiveness in plants | journal=[[Journal of Ecology]] | volume=99 | issue= 5| pages=1108–1115 | date=2011-03-28 | doi=10.1111/j.1365-2745.2011.01838.x | s2cid=38197332 | url=https://semanticscholar.org/paper/96c0953eb8acf2f150297ec574361c39215f0e68 }}</ref> Polyploidy may be associated with increased vigor and adaptability.<ref name="Gilbert">{{cite journal | last=Gilbert | first=Natasha | title=Ecologists find genomic clues to invasive and endangered plants | journal=Nature | date=2011-04-06 | url=http://www.nature.com/news/2011/110406/full/news.2011.213.html#B1 | doi=10.1038/news.2011.213 | access-date=2011-04-07 }}</ref> Some studies suggest that selection is more likely to favor diploidy in host species and haploidy in parasite species.<ref>{{cite journal |author1=Nuismer S. |author2=Otto S.P. | year=2004 | title=Host-parasite interactions and the evolution of ploidy | journal=Proc. Natl. Acad. Sci. USA | volume=101 | issue=30 | pages=11036–11039 | doi=10.1073/pnas.0403151101|pmid=15252199 | pmc=503737 | bibcode=2004PNAS..10111036N }}</ref>

When a germ cell with an uneven number of chromosomes undergoes meiosis, the chromosomes cannot be evenly divided between the daughter cells, resulting in [[aneuploid]] gametes. Triploid organisms, for instance, are usually sterile. Because of this, triploidy is commonly exploited in agriculture to produce seedless fruit such as bananas and watermelons. If the fertilization of human gametes results in three sets of chromosomes, the condition is called [[triploid syndrome]].

==Glossary of ploidy numbers==

{| class="wikitable"
! style="text-align:left" | Term !! style="text-align:left" |Description
|-
|'''Ploidy number''' || Number of chromosome sets
|-
|'''Monoploid number''' (''x'') || Number of chromosomes found in a single complete set
|-
|'''Chromosome number''' || Total number of chromosomes in all sets combined
|-
|'''Zygotic number''' || Number of chromosomes in zygotic cells
|-
|'''Haploid or gametic number''' (''n'') || Number of chromosomes found in gametes
|-
|'''Diploid number''' || Chromosome number of a diploid organism
|-
|'''Tetraploid number''' || Chromosome number of a tetraploid organism
|}

The common [[potato]] (''Solanum tuberosum'') is an example of a tetraploid organism, carrying four sets of chromosomes. During sexual reproduction, each potato plant inherits two sets of 12 chromosomes from the pollen parent, and two sets of 12 chromosomes from the ovule parent. The four sets combined provide a full complement of 48 chromosomes. The haploid number (half of 48) is 24. The monoploid number equals the total chromosome number divided by the ploidy level of the somatic cells: 48 chromosomes in total divided by a ploidy level of 4 equals a monoploid number of 12. Hence, the monoploid number (12) and haploid number (24) are distinct in this example.

However, commercial potato crops (as well as many other crop plants) are commonly propagated [[Vegetative reproduction|vegetatively]] (by asexual reproduction through mitosis),<ref>{{cite web |url=http://www.inspection.gc.ca/plants/plants-with-novel-traits/applicants/directive-94-08/biology-documents/solanum-tuberosum-l-/eng/1330982063974/1330982145930#a41 |title=The Biology of Solanum tuberosum (L.) (Potatoes) |publisher=Canadian Food Inspection Agency|date=2012-03-05 }}</ref> in which case new individuals are produced from a single parent, without the involvement of gametes and fertilization, and all the offspring are genetically identical to each other and to the parent, including in chromosome number. The parents of these vegetative clones may still be capable of producing haploid gametes in preparation for sexual reproduction, but these gametes are not used to create the vegetative offspring by this route.

==Specific examples==
Some eukaryotic genome-scale or [[genome size]] databases and other sources which may list the ploidy levels of many organisms:

xxxx<ref>{{cite journal |author1=Nuismer S. |author2=Otto S.P. | year=2004 | title=Host-parasite interactions and the evolution of ploidy | journal=Proc. Natl. Acad. Sci. USA | volume=101 | issue= 30| pages=11036–11039 | doi=10.1073/pnas.0403151101|pmid=15252199 | pmc=503737 | bibcode=2004PNAS..10111036N }}</ref>

{| class="wikitable"
|+ style="text-align:left" | Examples of various ploidy levels in species with x=11
|-
! style="text-align:left" | Species !! style="text-align:left" | Ploidy !! style="text-align:left" | Number of chromosomes
|-
| ''[[Eucalyptus]]'' spp. || Diploid || 2''n'' = 2''x'' = 22
|-
| [[Banana]] (''[[Musa (genus)|Musa]]'' spp.) || Triploid || 2''n'' = 3''x'' = 33
|-
| ''[[Coffea arabica]]'' || Tetraploid || 2''n'' = 4''x'' = 44
|-
| ''[[Sequoia sempervirens]]'' || Hexaploid || 2''n'' = 6''x'' = 66
|-
| ''[[Opuntia ficus-indica]]'' || Octoploid || 2''n'' = 8''x'' = 88
|}

{| class="wikitable"
|+ style="text-align:left" | List of common organisms by chromosome count
|-
! style="text-align:left" | Species !! style="text-align:left" | Number of chromosomes !! style="text-align:left" | Ploidy number
|-
|Vinegar/fruit fly || 8 || 2
|-
|Wheat || 14, 28 or 42 || 2, 4 or 6
|-
|Crocodilian || 32, 34, or 42 || 2
|-
|Apple || 34, 51, or 68 || 2, 3 or 4
|-
|Human || 46 || 2
|-
|Horse || 64 || 2
|-
|Chicken || 78 || 2
|-
|Gold fish || 100 or more || 2 or polyploid
|}
------------------------>
==Notas==
{{notelist}}
==Referências==
{{reflist |30em}}
==Bibliografia==
*Griffiths, A. J. ''et al.'' 2000. ''An introduction to genetic analysis'', 7th ed. W. H. Freeman, New York {{ISBN |0-7167-3520-2}}
=={{Links}}==
*[http://www.genomesize.com/ Animal genome size database]
*[https://web.archive.org/web/20050901105257/http://www.rbgkew.org.uk/cval/homepage.html Plant genome size database]
*[http://www.zbi.ee/fungal-genomesize/ Fungal genome size database]
*[http://protists.ensembl.org/index.html Protist genome-scale database] of [[Ensembl Genomes]]
*[http://www.pnas.org/content/suppl/2004/07/13/0403151101.DC1/03151DataSet1.pdf Supporting Data Set], with information on ploidy level and number of chromosomes of several protists)
*[https://www.youtube.com/watch?v=GfxJi2BUvNI Chromosome number and ploidy mutations] YouTube tutorial video


{{Cromossomos}}
{{Cromossomos}}


[[Categoria:Genética]]
[[Categoria:Genética]]
[[Categoria:Genética clássica]]
[[Categoria:Citogenética]]
[[Categoria:Conceitos de genética]]

Revisão das 12h36min de 13 de dezembro de 2020

Um conjunto haplóide que consiste num único grupo completo de cromossomas (igual ao conjunto monoplóide), conforme mostrado na figura acima, deve pertencer a uma espécie diplóide. Se um conjunto haplóide consiste em dois grupos, deve ser de uma espécie tetraplóide (quatro conjuntos).[1]

Ploidia é o número de conjuntos completos de cromossomas presentes numa célula e, em consequência, o número de alelos possíveis para o conjunto de genes autossómicos e pseudo-autossómicos nela existentes. Células somáticas, tecidos e organismos indivíduais podem ser descritos de acordo com o número de conjuntos de cromossomas presentes, o seu nível de ploidia, como monoplóide (1 conjunto), diploide (2 conjuntos), triploide (3 conjuntos), tetraploide (4 conjuntos), pentaploide (5 conjuntos), e assim por diante.[2][3] O termo genérico poliploide é frequentemente utilizado para descrever situações em que estejam presentes três ou mais conjuntos de cromossomas.[4][5]

Descrição

Cada espécie possui um número característico de cromossomos, nos seres humanos esse conjunto esta representado em dose dupla (diploide). Mas existem algumas espécies que o conjunto básico de cromossomos está em múltiplas cópias (poliploides). Porém, quando se considera a ploidia, um conjunto básico de cromossomos é chamado haplóide,como o caso de algumas bactérias ou leveduras, que têm fases haplóides da sua vida, (x), pois inclui apenas um cromossomo de cada tipo. A ploidia pode ser definida, portanto, como número de pares de cromossomos homólogos (cromossomos que têm informação para os mesmos genes e tem o mesmo tamanho) que cada célula apresenta.

Todos os seres têm fases haplóides como diplóides, assim como o ser-humano. Através da duração dessas fases podemos caracterizar o tipo de ciclo celular: haplonte (se a maior parte da vida do ser é passada como haplóide), diplonte (se a maior parte da vida do ser é passado como diplóide) ou haplodiplonte (se a vida do ser é dividida em fase haplonte e diplonte).

Grau de ploidia é número de genomas ou complementos cromossômicos de uma espécie. Os seres humanos são diplóides, pois possuimos 23 PARES de cromossomos. Porem nossos gametas (espermatozoide e ovulo) são células haplóides porque cada um possui somente 23 cromossomos.

Cada espécie em particular possuí um número de cromossomas característico. As espécies que se reproduzem assexuadamente têm um conjunto de cromossomas, que é igual em todas as células do corpo. As espécies que se reproduzem sexuadamente têm células somáticas, que são diplóides [2n] (têm dois conjuntos de cromossomas, um proveniente da mãe e outro do pai) ou poliplóides [Xn] (têm mais do que dois conjuntos de cromossomas). Além das células somáticas, os organismos que se reproduzem sexuadamente possuem os gâmetas (células reprodutoras), que são haplóides [n] (têm apenas um conjunto de cromossomas).

Os gâmetas são produzidos por meiose de uma célula diplóide da linha germinativa. Durante a meiose, cromossomas semelhantes de origem materna e paterna (por exemplo o cromossoma 1 de origem materna com o cromossoma 1 de origem paterna) podem trocar pequenas partes de si próprios (crossing-over), e assim criar novos cromossomas que não foram herdados unicamente de um dos progenitores (podendo criar, por exemplo, um cromossoma 1 que apresenta regiões provenientes do cromossoma 1 de origem materna junto com outras regiões do cromossoma 1 de origem paterna). Quando um gâmeta masculino e um gâmeta feminino se unem (fertilização), forma-se um novo organismo diplóide.

Notas

Referências

  1. ↑ Daniel Hartl (2011). Essential Genetics: A Genomics Perspective. [S.l.]: Jones & Bartlett Learning. 177 páginas. ISBN 978-0-7637-7364-9 
  2. ↑ U. R. Murty (1973). «Morphology of pachytene chromosomes and its bearing on the nature of polyploidy in the cytological races of Apluda mutica L.». Genetica. 44 (2): 234–243. doi:10.1007/bf00119108 
  3. ↑ Tuguo Tateoka (May 1975). «A contribution to the taxonomy of the Agrostis mertensii-flaccida complex (Poaceae) in Japan». Journal of Plant Research. 88 (2): 65–87. doi:10.1007/bf02491243  Verifique data em: |data= (ajuda)
  4. ↑ Rieger, R.; Michaelis, A.; Green, M.M. (1976). Glossary of Genetics and Cytogenetics: Classical and Molecular 4th ed. Berlin/Heidelberg: Springer-Verlag. p. 434. ISBN 978-3-540-07668-1. doi:10.1007/978-3-642-96327-8 
  5. ↑ Darlington, C. D. (Cyril Dean) (1937). Recent advances in cytology. Philadelphia: P. Blakiston's son & co. p. 60 

Bibliografia

  • Griffiths, A. J. et al. 2000. An introduction to genetic analysis, 7th ed. W. H. Freeman, New York ISBN 0-7167-3520-2

Ligações externas

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