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Ploidy (/ˈplɔɪdi/) is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here sets of chromosomes refers to the number of maternal and paternal chromosome copies, respectively, in each homologous chromosome pair—the form in which chromosomes naturally exist. Somatic cells, tissues, and individual organisms can be described according to the number of sets of chromosomes present (the "ploidy level"): monoploid (1 set), diploid (2 sets), triploid (3 sets), tetraploid (4 sets), pentaploid (5 sets), hexaploid (6 sets), heptaploid^[2] or septaploid^[3] (7 sets), etc. The generic term polyploid is often used to describe cells with three or more sets of chromosomes.^[4]^[5]

Virtually all 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.^[6] 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 insects), and in others entire tissues and organ systems may be polyploid despite the rest of the body being diploid (as in the mammalian liver^{[citation needed]}). 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.^[7] 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.^[8]^[9]

Humans are diploid organisms, normally carrying two complete sets of chromosomes in their somatic cells: one copy of paternal and maternal chromosomes, respectively, in each of the 23 homologous pairs of chromosomes that humans normally have. This results in two homologous pairs within each of the 23 homologous pairs, providing a full complement of 46 chromosomes. This total number of individual chromosomes (counting all complete sets) is called the chromosome number or chromosome complement. 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, with one paternal and maternal copy in each chromosome pair. 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. Euploidy and aneuploidy describe having a number of chromosomes that is an exact multiple of the number of chromosomes in a normal gamete; and having any other number, respectively. For example, a person with Turner syndrome may be missing one sex chromosome (X or Y), resulting in a (45,X) karyotype instead of the usual (46,XX) or (46,XY). This is a type of aneuploidy and cells from the person may be said to be aneuploid with a (diploid) chromosome complement of 45.

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").^[a] The principal meaning of the Greek word ᾰ̔πλόος (haplóos) is "single",^[10] from ἁ- (ha-, "one, same").^[11] διπλόος (diplóos) means "duplex" or "two-fold". Diploid therefore means "duplex-shaped" (compare "humanoid", "human-shaped").

Polish-German botanist Eduard Strasburger coined the terms haploid and diploid in 1905.^[b] Some authors suggest that Strasburger based the terms on August Weismann's conception of the id (or germ plasm),^[14]^[15]^[16] 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.^[17]^{[citation needed]}

Types of ploidy

Haploid and monoploid

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.^[18] 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.^{[citation needed]}

An alternative usage defines "haploid" as having a single copy of each chromosome – that is, one and only one set of chromosomes.^[19] In this case, the nucleus of a eukaryotic cell is said to be haploid only if it has a single set of chromosomes, 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.^{[citation needed]}

Gametes (sperm and ova) are haploid cells. The haploid gametes produced by most organisms combine to form a zygote with n pairs of chromosomes, i.e. 2n 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. 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.^[20]

All plants and many fungi and algae 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 mosses. 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.^{[citation needed]}

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,^[21] also known as basic or cardinal number,^[22] or fundamental number.^[23]^[24] 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 × 7 = 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 2n = 6x = 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 = 3x).^[25]

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 = n = 23.

Diploid

Diploid cells have two 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)^[26] have been regarded as the only known exceptions (as of 2004).^[27] However, some genetic studies have rejected any polyploidism in mammals as unlikely, and suggest that amplification and dispersion of repetitive sequences best explain the large genome size of these two rodents.^[28] All normal diploid individuals have some small fraction of cells that display polyploidy. Human diploid cells have 46 chromosomes (the somatic number, 2n) and human haploid gametes (egg and sperm) have 23 chromosomes (n). Retroviruses 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.^[29]

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^[2] or septaploid^[3] (7 sets), octoploid (8 sets), nonaploid (9 sets), decaploid (10 sets), undecaploid (11 sets), dodecaploid (12 sets), tridecaploid (13 sets), tetradecaploid (14 sets), etc.^[30]^[31]^[32]^[33] Some higher ploidies include hexadecaploid (16 sets), dotriacontaploid (32 sets), and tetrahexacontaploid (64 sets),^[34] though Greek terminology may be set aside for readability in cases of higher ploidy (such as "16-ploid").^[32] Polytene chromosomes of plants and fruit flies can be 1024-ploid.^[35]^[36] 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.^[37]

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.^[38] The so-called Brassica triangle is an example of allopolyploidy, where three different parent species have hybridized in all possible pair combinations to produce three new species.^[39]

Polyploidy occurs commonly in plants, but rarely in animals. Even in diploid organisms, many somatic cells 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.^{[citation needed]}

It is possible for polyploid organisms to revert to lower ploidy by haploidisation.^{[citation needed]}

In bacteria and archaea

Polyploidy is a characteristic of the bacterium Deinococcus radiodurans ^[40] and of the archaeon Halobacterium salinarum.^[41] These two species are highly resistant to ionizing radiation and desiccation, conditions that induce DNA double-strand breaks.^[42]^[43] This resistance appears to be due to efficient homologous recombinational repair.

Variable or indefinite ploidy

Depending on growth conditions, prokaryotes 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.^{[citation needed]}

In ciliates, the macronucleus is called ampliploid, because only part of the genome is amplified.^[44]

Mixoploidy

Mixoploidy is the case where two cell lines, one diploid and one polyploid, coexist within the same organism. Though polyploidy in humans is not viable, mixoploidy has been found in live adults and children.^[45] There are two types: diploid-triploid mixoploidy, in which some cells have 46 chromosomes and some have 69,^[46] 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

Dihaploid and polyhaploid cells are formed by haploidisation of polyploids, i.e., by halving the chromosome constitution.^{[citation needed]}

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.^{[citation needed]}

The term "dihaploid" was coined by Bender^[47] to combine in one word the number of genome copies (diploid) and their origin (haploid). The term is well established in this original sense,^[48]^[49] but it has also been used for doubled monoploids or doubled haploids, which are homozygous and used for genetic research.^[50]

Euploidy and aneuploidy

Euploidy (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-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 karyotypes would consequentially be a multiple of the haploid number, which in humans is 23.^{[citation needed]}

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 have only one sex chromosome). Aneuploid karyotypes are given names with the suffix -somy (rather than -ploidy, used for euploid karyotypes), such as trisomy and monosomy.^{[citation needed]}

Homoploid

Homoploid means "at the same ploidy level", i.e. having the same number of homologous chromosomes. For example, homoploid 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]}

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.^[51]^[52] 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 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,^[37] 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.^[53]

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.^[8] 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.^{[citation needed]}

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, 2n = 6x = 42 (where the monoploid number x = 7 and the haploid number n = 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]}

Tetraploidy (four sets of chromosomes, 2n = 4x) is common in many plant species, and also occurs in amphibians, reptiles, and insects. For example, species of Xenopus (African toads) form a ploidy series, featuring diploid (X. tropicalis, 2n=20), tetraploid (X. laevis, 4n=36), octaploid (X. wittei, 8n=72), and dodecaploid (X. ruwenzoriensis, 12n=108) species.^[54]

Over evolutionary time scales in which chromosomal polymorphisms 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.^{[citation needed]}

Haplodiploidy

Ploidy can also vary between individuals of the same species or at different stages of the life cycle.^[55]^[56] In some insects it differs by caste. In humans, only the gametes are haploid, but in many of the social insects, including ants, bees, and termites, males develop from unfertilized eggs, making them haploid for their entire lives, even as adults.^{[citation needed]}

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.^[57] In Entamoeba, the ploidy level varies from 4n to 40n in a single population.^[58] Alternation of generations occurs in most plants, with individuals "alternating" ploidy level between different stages of their sexual life cycle.^{[citation needed]}

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.^[59]

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.^[60] Polyploidy may be associated with increased vigor and adaptability.^[61] Some studies suggest that selection is more likely to favor diploidy in host species and haploidy in parasite species.^[62] However, polyploidization is associated with an increase in transposable element content^[63]^[64] and relaxed purifying selection on recessive deleterious alleles.^[65]^[66]

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.^{[citation needed]}

In unicellular organisms the ploidy nutrient limitation hypothesis suggests that nutrient limitation should encourage haploidy in preference to higher ploidies. This hypothesis is due to the higher surface-to-volume ratio of haploids, which eases nutrient uptake, thereby increasing the internal nutrient-to-demand ratio. Mable 2001 finds Saccharomyces cerevisiae to be somewhat inconsistent with this hypothesis however, as haploid growth is faster than diploid under high nutrient conditions. The NLH is also tested in haploid, diploid, and polyploid fungi by Gerstein et al. 2017. This result is also more complex: On the one hand, under phosphorus and other nutrient limitation, lower ploidy is selected as expected. However under normal nutrient levels or under limitation of only nitrogen, higher ploidy was selected. Thus the NLH – and more generally, the idea that haploidy is selected by harsher conditions – is cast into doubt by these results.^[67]

Older WGDs have also been investigated. Only as recently as 2015 was the ancient whole genome duplication in Baker's yeast proven to be allopolyploid, by Marcet-Houben and Gabaldón 2015. It still remains to be explained why there are not more polyploid events in fungi, and the place of neopolyploidy and mesopolyploidy in fungal history.^[67]

Less efficient natural selection in diploid compared to haploid tissue

The concept that those genes of an organism that are expressed exclusively in the diploid stage are under less efficient natural selection than those genes expressed in the haploid stage is referred to as the “masking theory”.^[68] Evidence in support of this masking theory has been reported in studies of the single-celled yeast Saccharomyces cerevisiae.^[69] In further support of the masking theory, evidence of strong purifying selection in haploid tissue-specific genes has been reported for the plant Scots Pine.^[68]

Glossary of ploidy numbers

Term	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.^{[citation needed]}

However, commercial potato crops (as well as many other crop plants) are commonly propagated vegetatively (by asexual reproduction through mitosis),^[70] 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

Examples of various ploidy levels in species with x=11
Species	Ploidy	Number of chromosomes
Eucalyptus spp.	Diploid	2x = 22
Banana (Musa spp.)	Triploid	3x = 33
Coffea arabica	Tetraploid	4x = 44
Sequoia sempervirens	Hexaploid	6x = 66
Opuntia ficus-indica	Octoploid	8x = 88

List of common organisms by chromosome count
Species	Number of chromosomes	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

Notes

^ Compare the etymology of tuple, from the Latin for "-fold".
^ 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."^[12]^[13]

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^ Simon Renny-Byfield; et al. (2010). "Flow cytometry and GISH reveal mixed ploidy populations and Spartina nonaploids with genomes of S. alterniflora and S. maritima origin". Annals of Botany. 105 (4): 527–533. doi:10.1093/aob/mcq008. PMC 2850792. PMID 20150197.
^ ^a ^b Kim E. Hummer; et al. (March 2009). "Decaploidy in Fragaria iturupensis (Rosaceae)". Am. J. Bot. 96 (3): 713–716. doi:10.3732/ajb.0800285. PMID 21628226.
^ Talyshinskiĭ, G. M. (1990). "Study of the fractional composition of the proteins in the compound fruit of polyploid mulberry". Shelk (5): 8–10.
^ Fujikawa-Yamamoto K (2001). "Temperature dependence in Proliferation of tetraploid Meth-A cells in comparison with the parent diploid cells". Cell Structure and Function. 26 (5): 263–269. doi:10.1247/csf.26.263. PMID 11831358.
^ Kiichi Fukui; Shigeki Nakayama (1996). Plant Chromosomes: Laboratory Methods. CRC Press. ISBN 9780849389191.
^ "Genes involved in tissue and organ development: Polytene chromosomes, endoreduplication and puffing". The Interactive Fly. Archived from the original on 2005-05-04. Retrieved 2012-12-16.
^ ^a ^b Encyclopedia of the Life Sciences (2002) "Polyploidy" Francesco D'Amato and Mauro Durante
^ Ramsey, Justin; Schemske, Douglas W. (November 2002). "Neopolyploidy in Flowering Plants". Annual Review of Ecology and Systematics. 33 (1): 589–639. doi:10.1146/annurev.ecolsys.33.010802.150437.
^ Song, Xiaoming; Wei, Yanping; Xiao, Dong; Gong, Ke; Sun, Pengchuan; Ren, Yiming; Yuan, Jiaqing; Wu, Tong; Yang, Qihang; Li, Xinyu; Nie, Fulei; Li, Nan; Feng, Shuyan; Pei, Qiaoying; Yu, Tong (2021-02-04). "Brassica carinata genome characterization clarifies U's triangle model of evolution and polyploidy in Brassica". Plant Physiology. 186 (1): 388–406. doi:10.1093/plphys/kiab048. ISSN 0032-0889. PMC 8154070. PMID 33599732.
^ Hansen MT (1978). "Multiplicity of genome equivalents in the radiation-resistant bacterium Micrococcus radiodurans". J. Bacteriol. 134 (1): 71–75. doi:10.1128/JB.134.1.71-75.1978. PMC 222219. PMID 649572.
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^ James B. Anderson; Linda M Kohn. "Dikaryons, diploids, and evolution" (PDF). University of Toronto. Archived from the original (PDF) on 2013-05-27. Retrieved 2012-12-16.
^ Schmid, M; Evans, BJ; Bogart, JP (2015). "Polyploidy in Amphibia". Cytogenet. Genome Res. 145 (3–4): 315–330. doi:10.1159/000431388. PMID 26112701.
^ Parfrey LW, Lahr DJ, Katz LA (2008). "The dynamic nature of eukaryotic genomes". Mol Biol Evol. 25 (4): 787–794. doi:10.1093/molbev/msn032. PMC 2933061. PMID 18258610.
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^ Baduel, Pierre; Quadrana, Leandro; Hunter, Ben; Bomblies, Kirsten; Colot, Vincent (2019-12-20). "Relaxed purifying selection in autopolyploids drives transposable element over-accumulation which provides variants for local adaptation". Nature Communications. 10 (1): 5818. Bibcode:2019NatCo..10.5818B. doi:10.1038/s41467-019-13730-0. ISSN 2041-1723. PMC 6925279. PMID 31862875. S2CID 209420359.
^ ^a ^b Blischak, Paul D.; Mabry, Makenzie E.; Conant, Gavin C.; Pires, J. Chris (2018-11-02). "Integrating Networks, Phylogenomics, and Population Genomics for the Study of Polyploidy". Annual Review of Ecology, Evolution, and Systematics. 49 (1). Annual Reviews: 253–278. doi:10.1146/annurev-ecolsys-121415-032302. ISSN 1543-592X. S2CID 92205236.
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Sources

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

External links

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

Animal genome size database
Plant genome size database
Fungal genome size database
Protist genome-scale database of Ensembl Genomes
Nuismer S.; Otto S.P. (2004). "Host-parasite interactions and the evolution of ploidy". Proc. Natl. Acad. Sci. USA. 101 (30): 11036–11039. Bibcode:2004PNAS..10111036N. doi:10.1073/pnas.0403151101. PMC 503737. PMID 15252199. (Supporting Data Set, with information on ploidy level and number of chromosomes of several protists)
Chromosome number and ploidy mutations YouTube tutorial video

[10] Compare the etymology of tuple, from the Latin for "-fold".

[15] 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."^[12]^[13]

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[Svartman-2005-30] Svartman, Marta; Stone, Gary; Stanyon, Roscoe (2005). "Molecular cytogenetics discards polyploidy in mammals". Genomics. 85 (4): 425–430. doi:10.1016/j.ygeno.2004.12.004. PMID 15780745.

[31] "Human Retroviruses". Archived from the original on 2003-03-30. Retrieved 2008-05-14.

[Dierschke-2009-32] Dierschke T, Mandáková T, Lysak MA, Mummenhoff K (September 2009). "A bicontinental origin of polyploid Australian/New Zealand Lepidium species (Brassicaceae)? Evidence from genomic in situ hybridization". Annals of Botany. 104 (4): 681–688. doi:10.1093/aob/mcp161. PMC 2729636. PMID 19589857.

[Renny-Byfield-2010-33] Simon Renny-Byfield; et al. (2010). "Flow cytometry and GISH reveal mixed ploidy populations and Spartina nonaploids with genomes of S. alterniflora and S. maritima origin". Annals of Botany. 105 (4): 527–533. doi:10.1093/aob/mcq008. PMC 2850792. PMID 20150197.

[Hummer-2009-34] Kim E. Hummer; et al. (March 2009). "Decaploidy in Fragaria iturupensis (Rosaceae)". Am. J. Bot. 96 (3): 713–716. doi:10.3732/ajb.0800285. PMID 21628226.

[Talyshinskiĭ-1990-35] Talyshinskiĭ, G. M. (1990). "Study of the fractional composition of the proteins in the compound fruit of polyploid mulberry". Shelk (5): 8–10.

[36] Fujikawa-Yamamoto K (2001). "Temperature dependence in Proliferation of tetraploid Meth-A cells in comparison with the parent diploid cells". Cell Structure and Function. 26 (5): 263–269. doi:10.1247/csf.26.263. PMID 11831358.

[37] Kiichi Fukui; Shigeki Nakayama (1996). Plant Chromosomes: Laboratory Methods. CRC Press. ISBN 9780849389191.

[38] "Genes involved in tissue and organ development: Polytene chromosomes, endoreduplication and puffing". The Interactive Fly. Archived from the original on 2005-05-04. Retrieved 2012-12-16.

[D'Amato-2002-39] Encyclopedia of the Life Sciences (2002) "Polyploidy" Francesco D'Amato and Mauro Durante

[40] Ramsey, Justin; Schemske, Douglas W. (November 2002). "Neopolyploidy in Flowering Plants". Annual Review of Ecology and Systematics. 33 (1): 589–639. doi:10.1146/annurev.ecolsys.33.010802.150437.

[41] Song, Xiaoming; Wei, Yanping; Xiao, Dong; Gong, Ke; Sun, Pengchuan; Ren, Yiming; Yuan, Jiaqing; Wu, Tong; Yang, Qihang; Li, Xinyu; Nie, Fulei; Li, Nan; Feng, Shuyan; Pei, Qiaoying; Yu, Tong (2021-02-04). "Brassica carinata genome characterization clarifies U's triangle model of evolution and polyploidy in Brassica". Plant Physiology. 186 (1): 388–406. doi:10.1093/plphys/kiab048. ISSN 0032-0889. PMC 8154070. PMID 33599732.

[Hansen-1978-42] Hansen MT (1978). "Multiplicity of genome equivalents in the radiation-resistant bacterium Micrococcus radiodurans". J. Bacteriol. 134 (1): 71–75. doi:10.1128/JB.134.1.71-75.1978. PMC 222219. PMID 649572.

[Soppa-2011-43] Soppa J (2011). "Ploidy and gene conversion in Archaea". Biochem. Soc. Trans. 39 (1): 150–154. doi:10.1042/BST0390150. PMID 21265763. S2CID 31385928.

[Zahradka-2006-44] Zahradka K, Slade D, Bailone A, Sommer S, Averbeck D, Petranovic M, Lindner AB, Radman M (2006). "Reassembly of shattered chromosomes in Deinococcus radiodurans". Nature. 443 (7111): 569–573. Bibcode:2006Natur.443..569Z. doi:10.1038/nature05160. PMID 17006450. S2CID 4412830.

[Kottemann-2005-45] Kottemann M, Kish A, Iloanusi C, Bjork S, DiRuggiero J (2005). "Physiological responses of the halophilic archaeon Halobacterium sp. strain NRC1 to desiccation and gamma irradiation" (PDF). Extremophiles. 9 (3): 219–227. doi:10.1007/s00792-005-0437-4. PMID 15844015. S2CID 8391234.

[46] Schaechter, M. Eukaryotic microbes. Amsterdam, Academic Press, 2012, p. 217.

[47] Edwards MJ; et al. (1994). "Mixoploidy in humans: two surviving cases of diploid-tetraploid mixoploidy and comparison with diploid-triploid mixoploidy". Am J Med Genet. 52 (3): 324–330. doi:10.1002/ajmg.1320520314. PMID 7810564.

[48] Järvelä, IE; Salo, MK; Santavuori, P; Salonen, RK (1993). "46,XX/69,XXX diploid-triploid mixoploidy with hypothyroidism and precocious puberty". J Med Genet. 30 (11): 966–967. doi:10.1136/jmg.30.11.966. PMC 1016611. PMID 8301657.

[49] Bender K (1963). "Über die Erzeugung und Entstehung dihaploider Pflanzen bei Solanum tuberosum"". Zeitschrift für Pflanzenzüchtung. 50: 141–166.

[50] Nogler, G.A. 1984. Gametophytic apomixis. In Embryology of angiosperms. Edited by B.M. Johri. Springer, Berlin, Germany. pp. 475–518.

[51] * Pehu E (1996). "The current status of knowledge on the cellular biology of potato". Potato Research. 39 (3): 429–435. doi:10.1007/bf02357948. S2CID 32122774.

[52] * Sprague G.F.; Russell W.A.; Penny L.H. (1960). "Mutations affecting quantitative traits in the selfed progeny of double monoploid maize stocks". Genetics. 45 (7): 855–866. doi:10.1093/genetics/45.7.855. PMC 1210096. PMID 17247970.

[53] Books, Elsevier Science & Technology (1950). Advances in Genetics. Academic Press. ISBN 978-0-12-017603-8.

[Cosín-2011-54] Cosín, Darío J. Díaz; Novo, Marta; Fernández, Rosa (2011). "Reproduction of Earthworms: Sexual Selection and Parthenogenesis". Biology of Earthworms. Soil Biology. Vol. 24. pp. 69–86. doi:10.1007/978-3-642-14636-7_5. ISBN 978-3-642-14635-0.

[55] James B. Anderson; Linda M Kohn. "Dikaryons, diploids, and evolution" (PDF). University of Toronto. Archived from the original (PDF) on 2013-05-27. Retrieved 2012-12-16.

[56] Schmid, M; Evans, BJ; Bogart, JP (2015). "Polyploidy in Amphibia". Cytogenet. Genome Res. 145 (3–4): 315–330. doi:10.1159/000431388. PMID 26112701.

[57] Parfrey LW, Lahr DJ, Katz LA (2008). "The dynamic nature of eukaryotic genomes". Mol Biol Evol. 25 (4): 787–794. doi:10.1093/molbev/msn032. PMC 2933061. PMID 18258610.

[58] Qiu Y.-L., Taylor A. B., McManus H. A. (2012). "Evolution of the life cycle in land plants" (PDF). Journal of Systematics and Evolution. 50 (3): 171–194. doi:10.1111/j.1759-6831.2012.00188.x. hdl:2027.42/92043. S2CID 40564254.{{cite journal}}: CS1 maint: multiple names: authors list (link)

[59] Crosland MW, Crozier RH (1986). "Myrmecia pilosula, an Ant with Only One Pair of Chromosomes". Science. 231 (4743): 1278. Bibcode:1986Sci...231.1278C. doi:10.1126/science.231.4743.1278. PMID 17839565. S2CID 25465053.

[60] "Archived copy" (PDF). Archived from the original (PDF) on 2014-02-23. Retrieved 2014-02-18.{{cite web}}: CS1 maint: archived copy as title (link)

[61] John O. Oberpriller; A Mauro (1991). The Development and Regenerative Potential of Cardiac Muscle. Taylor&Francis. ISBN 9783718605187.

[Pandit-2011-62] Pandit, M. K.; Pocock, M. J. O.; Kunin, W. E. (2011-03-28). "Ploidy influences rarity and invasiveness in plants". Journal of Ecology. 99 (5): 1108–1115. Bibcode:2011JEcol..99.1108P. doi:10.1111/j.1365-2745.2011.01838.x. S2CID 38197332.

[Gilbert-2011-63] Gilbert, Natasha (2011-04-06). "Ecologists find genomic clues to invasive and endangered plants". Nature. doi:10.1038/news.2011.213. Retrieved 2011-04-07.

[64] Nuismer S.; Otto S.P. (2004). "Host-parasite interactions and the evolution of ploidy". Proc. Natl. Acad. Sci. USA. 101 (30): 11036–11039. Bibcode:2004PNAS..10111036N. doi:10.1073/pnas.0403151101. PMC 503737. PMID 15252199.

[65] McClintock, B. (1984-11-16). "The significance of responses of the genome to challenge". Science. 226 (4676): 792–801. Bibcode:1984Sci...226..792M. doi:10.1126/science.15739260. ISSN 0036-8075. PMID 15739260.

[66] Matzke, M.A; Matzke, A.J.M (June 1998). "Polyploidy and transposons". Trends in Ecology & Evolution. 13 (6): 241. Bibcode:1998TEcoE..13R.241M. doi:10.1016/s0169-5347(98)01390-1. ISSN 0169-5347. PMID 21238281.

[67] Ronfort, J. (August 1999). "The mutation load under tetrasomic inheritance and its consequences for the evolution of the selfing rate in autotetraploid species". Genetics Research. 74 (1): 31–42. doi:10.1017/S0016672399003845. ISSN 1469-5073.

[68] Baduel, Pierre; Quadrana, Leandro; Hunter, Ben; Bomblies, Kirsten; Colot, Vincent (2019-12-20). "Relaxed purifying selection in autopolyploids drives transposable element over-accumulation which provides variants for local adaptation". Nature Communications. 10 (1): 5818. Bibcode:2019NatCo..10.5818B. doi:10.1038/s41467-019-13730-0. ISSN 2041-1723. PMC 6925279. PMID 31862875. S2CID 209420359.

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-{{short description|Number of sets of chromosomes in a cell}}
+{{short description|Number of sets of chromosomes of a cell}}
 {{See also|List of organisms by chromosome count|Chromosome#Number in various organisms}}
-[[File:Haploid vs diploid.svg|thumb|upright|A haploid set that consists of a single complete set of chromosomes (equal to the monoploid set), as shown in the picture above, must belong to a diploid species. If a haploid set consists of two sets, it must be of a tetraploid (four sets) species.<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>]]
+[[File:Haploid vs diploid.svg|thumb|upright|A haploid set that consists of a single complete set of chromosomes (equal to the monoploid set), as shown in the picture above, must belong to a diploid species. If a haploid set consists of two sets, it must be of a tetraploid (four sets) species.<ref name="Hartl-2011">{{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>]]
-'''Ploidy''' ({{IPAc-en|ˈ|p|l|ɔɪ|d|i}}) is the number of complete sets of [[chromosome]]s in a [[cell (biology)|cell]], and hence the number of possible [[allele]]s for [[Autosome|autosomal]] and [[Pseudoautosomal region|pseudoautosomal]] [[genes]]. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively, in each homologous chromosome pair, which chromosomes naturally exist as. [[Somatic cell]]s, [[Tissue (biology)|tissues]], and [[Individual#Biology|individual]] organisms can be described according to the number of sets of chromosomes present (the "ploidy level"): '''monoploid''' (1 set), '''diploid''' (2 sets), '''triploid''' (3 sets), '''tetraploid''' (4 sets), '''pentaploid''' (5 sets), '''hexaploid''' (6 sets), '''heptaploid'''<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> or '''septaploid'''<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> (7 sets), etc. The generic term [[polyploidy|polyploid]] is often used to describe cells with three or more sets of chromosomes.<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>
+'''Ploidy''' ({{IPAc-en|ˈ|p|l|ɔɪ|d|i}}) is the number of complete sets of [[chromosome]]s in a [[cell (biology)|cell]], and hence the number of possible [[allele]]s for [[Autosome|autosomal]] and [[Pseudoautosomal region|pseudoautosomal]] [[genes]]. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, respectively, in each homologous chromosome pair—the form in which chromosomes naturally exist. [[Somatic cell]]s, [[Tissue (biology)|tissues]], and [[Individual#Biology|individual]] organisms can be described according to the number of sets of chromosomes present (the "ploidy level"): '''monoploid''' (1 set), '''diploid''' (2 sets), '''triploid''' (3 sets), '''tetraploid''' (4 sets), '''pentaploid''' (5 sets), '''hexaploid''' (6 sets), '''heptaploid'''<ref name="Murty-1973">{{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> or '''septaploid'''<ref name="Tateoka-1975">{{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> (7 sets), etc. The generic term [[polyploidy|polyploid]] is often used to describe cells with three or more sets of chromosomes.<ref name="Rieger-1976">{{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-1937">{{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>
-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|doi-access=free}}</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>
+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="Snustad-2012">{{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]]{{Citation needed|date=May 2024}}). 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="Otto-2007">{{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|doi-access=free}}</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="Mable-2004">{{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="Madlung-2012">{{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, normally carrying two complete sets of chromosomes in their somatic cells: one copy of paternal and maternal chromosomes, respectively, in each of the 23 homologous pairs of chromosomes that humans normally have. This results in two homologous pairs within each of the 23 homologous pairs,  providing a full complement of 46 chromosomes. This total number of individual chromosomes (counting all complete sets) is called the '''chromosome number''' or '''chromosome complement'''. 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, with one paternal and maternal copy in each chromosome pair. 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. [[#Euploidy and aneuploidy|Euploidy and aneuploidy]] describe having a number of chromosomes that is an exact multiple of the number of chromosomes in a normal gamete; and having any other number, respectively. For example, a person with [[Turner syndrome]] may be missing one sex chromosome (X or Y), resulting in a (45,X) karyotype instead of the usual (46,XX) or (46,XY). This is a type of aneuploidy and cells from the person may be said to be aneuploid with a (diploid) chromosome complement of 45.
@@ Line 12: / Line 12: @@
 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=https://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=https://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}}
+Polish-German 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| bibcode=2008BotRv..74..395H | 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==
@@ Line 34: / Line 34: @@
 {{redirect|Diploid|the geometrical construct|Dyakis dodecahedron}}
 [[File:Human karyotype with bands and sub-bands.png|thumb|[[karyotype|Karyogram]] of a typical human cell, showing a diploid set of 22 [[Homologous chromosome|homologous]] [[autosomal]] chromosome pairs. It also shows both the female (XX) and male (XY) versions of the two [[sex chromosome]]s (at bottom right), as well as the [[human mitochondrial genetics|mitochondrial genome]] (to scale at bottom left). {{further|Karyotype}}]]
-'''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 | hdl=11336/102012 | hdl-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=Human Retroviruses |access-date=2008-05-14 |archive-url=https://archive.today/20030330094545/http://web.uct.ac.za/depts/mmi/jmoodie/hiv2.html |archive-date=2003-03-30 |url-status=dead }}</ref>
+'''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="Gallardo-2006">{{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 | hdl=11336/102012 | hdl-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=Human Retroviruses |access-date=2008-05-14 |archive-url=https://archive.today/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= |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 |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|doi-access=free }}</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 |publisher=CRC Press }}</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 />
+'''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="Murty-1973"/> or septaploid<ref name="Tateoka-1975"/> (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-2009">{{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-2010">{{cite journal |url= |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-2009">{{cite journal |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|doi-access=free }}</ref><ref name="Talyshinskiĭ-1990">{{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-2009" /> [[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 |publisher=CRC Press }}</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-2002" />
-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=Justin |last2=Schemske |first2=Douglas W. |title=Neopolyploidy in Flowering Plants |journal=Annual Review of Ecology and Systematics |date=November 2002 |volume=33 |issue=1 |pages=589–639 |doi=10.1146/annurev.ecolsys.33.010802.150437 }}</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.<ref>{{Cite journal |last=Song |first=Xiaoming |last2=Wei |first2=Yanping |last3=Xiao |first3=Dong |last4=Gong |first4=Ke |last5=Sun |first5=Pengchuan |last6=Ren |first6=Yiming |last7=Yuan |first7=Jiaqing |last8=Wu |first8=Tong |last9=Yang |first9=Qihang |last10=Li |first10=Xinyu |last11=Nie |first11=Fulei |last12=Li |first12=Nan |last13=Feng |first13=Shuyan |last14=Pei |first14=Qiaoying |last15=Yu |first15=Tong |date=2021-02-04 |title=Brassica carinata genome characterization clarifies U’s triangle model of evolution and polyploidy in Brassica |url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8154070/ |journal=Plant Physiology |volume=186 |issue=1 |pages=388–406 |doi=10.1093/plphys/kiab048 |issn=0032-0889 |pmc=8154070 |pmid=33599732}}</ref>
+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=Justin |last2=Schemske |first2=Douglas W. |title=Neopolyploidy in Flowering Plants |journal=Annual Review of Ecology and Systematics |date=November 2002 |volume=33 |issue=1 |pages=589–639 |doi=10.1146/annurev.ecolsys.33.010802.150437 }}</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.<ref>{{Cite journal |last1=Song |first1=Xiaoming |last2=Wei |first2=Yanping |last3=Xiao |first3=Dong |last4=Gong |first4=Ke |last5=Sun |first5=Pengchuan |last6=Ren |first6=Yiming |last7=Yuan |first7=Jiaqing |last8=Wu |first8=Tong |last9=Yang |first9=Qihang |last10=Li |first10=Xinyu |last11=Nie |first11=Fulei |last12=Li |first12=Nan |last13=Feng |first13=Shuyan |last14=Pei |first14=Qiaoying |last15=Yu |first15=Tong |date=2021-02-04 |title=Brassica carinata genome characterization clarifies U's triangle model of evolution and polyploidy in Brassica |journal=Plant Physiology |volume=186 |issue=1 |pages=388–406 |doi=10.1093/plphys/kiab048 |issn=0032-0889 |pmc=8154070 |pmid=33599732}}</ref>
 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.{{citation needed|date=May 2023}}
@@ Line 47: / Line 47: @@
 ====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 }}</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 |url=https://hal-mnhn.archives-ouvertes.fr/mnhn-02862359/file/2005_Kottemann_Kish_NRC1%20physiological%20response%20to%20desiccation%20and%20gamma%20radiation.pdf }}</ref> This resistance appears to be due to efficient [[homologous recombination]]al repair.
+[[Polyploid]]y is a characteristic of the bacterium ''[[Deinococcus radiodurans]]'' <ref name="Hansen-1978">{{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="Soppa-2011">{{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 }}</ref> These two species are highly resistant to [[ionizing radiation]] and [[desiccation]], conditions that induce [[DNA]] double-strand breaks.<ref name="Zahradka-2006">{{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="Kottemann-2005">{{cite journal |vauthors=Kottemann M, Kish A, Iloanusi C, Bjork S, DiRuggiero J |title=Physiological responses of the halophilic archaeon Halobacterium sp. strain NRC1 to desiccation and gamma irradiation |journal=Extremophiles |volume=9 |issue=3 |pages=219–227 |year=2005 |pmid=15844015 |doi=10.1007/s00792-005-0437-4 |s2cid=8391234 |url=https://hal-mnhn.archives-ouvertes.fr/mnhn-02862359/file/2005_Kottemann_Kish_NRC1%20physiological%20response%20to%20desiccation%20and%20gamma%20radiation.pdf }}</ref> This resistance appears to be due to efficient [[homologous recombination]]al repair.
 ===Variable or indefinite ploidy===
@@ Line 68: / Line 68: @@
 '''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.{{citation needed|date=May 2023}}
-'''[[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 have only one sex chromosome). Aneuploid [[karyotype]]s are given names with the suffix ''-somy'' (rather than ''-ploidy'', used for euploid karyotypes), such as [[trisomy]] and [[monosomy]].
+'''[[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 have only one sex chromosome). Aneuploid [[karyotype]]s are given names with the suffix ''-somy'' (rather than ''-ploidy'', used for euploid karyotypes), such as [[trisomy]] and [[monosomy]].{{cn|date=June 2024}}
 ===Homoploid===
@@ Line 74: / Line 74: @@
 ===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>{{cite book |doi=10.1007/978-3-642-14636-7_5  |chapter=Reproduction of Earthworms: Sexual Selection and Parthenogenesis |title=Biology of Earthworms |series=Soil Biology |year=2011 |last1=Cosín |first1=Darío J. Díaz |last2=Novo |first2=Marta |last3=Fernández |first3=Rosa |volume=24 |pages=69–86 |isbn=978-3-642-14635-0 }}</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.)
+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="Cosín-2011">{{cite book |doi=10.1007/978-3-642-14636-7_5  |chapter=Reproduction of Earthworms: Sexual Selection and Parthenogenesis |title=Biology of Earthworms |series=Soil Biology |year=2011 |last1=Cosín |first1=Darío J. Díaz |last2=Novo |first2=Marta |last3=Fernández |first3=Rosa |volume=24 |pages=69–86 |isbn=978-3-642-14635-0 }}</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>
+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-2002">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.{{citation needed|date=May 2023}}
+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="Mable-2004"/> 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.{{citation needed|date=May 2023}}
 [[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}}
@@ Line 88: / Line 88: @@
 [[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.
+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.{{cn|date=June 2024}}
 ===Haplodiploidy===
@@ Line 101: / Line 101: @@
 == 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 | doi-access=free }}</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 |doi-access=free }}</ref> However, polyploidization is associated with an increase in [[transposable element]] content<ref>{{Cite journal |last=McClintock |first=B. |date=1984-11-16 |title=The significance of responses of the genome to challenge |url=https://pubmed.ncbi.nlm.nih.gov/15739260/ |journal=Science |volume=226 |issue=4676 |pages=792–801 |doi=10.1126/science.15739260 |issn=0036-8075 |pmid=15739260|bibcode=1984Sci...226..792M }}</ref><ref>{{Cite journal |last1=Matzke |first1=M.A |last2=Matzke |first2=A.J.M |date=June 1998 |title=Polyploidy and transposons |url=https://doi.org/10.1016/S0169-5347(98)01390-1 |journal=Trends in Ecology & Evolution |volume=13 |issue=6 |pages=241 |doi=10.1016/s0169-5347(98)01390-1 |pmid=21238281 |issn=0169-5347}}</ref> and relaxed [[purifying selection]] on [[recessive]] deleterious alleles.<ref>{{Cite journal |last=Ronfort |first=J. |date=August 1999 |title=The mutation load under tetrasomic inheritance and its consequences for the evolution of the selfing rate in autotetraploid species |url=https://www.cambridge.org/core/journals/genetics-research/article/mutation-load-under-tetrasomic-inheritance-and-its-consequences-for-the-evolution-of-the-selfing-rate-in-autotetraploid-species/767EA01E7DFA1F44CC91BD49019D57E9 |journal=Genetics Research |language=en |volume=74 |issue=1 |pages=31–42 |doi=10.1017/S0016672399003845 |issn=1469-5073|doi-access=free }}</ref><ref>{{Cite journal |last1=Baduel |first1=Pierre |last2=Quadrana |first2=Leandro |last3=Hunter |first3=Ben |last4=Bomblies |first4=Kirsten |last5=Colot |first5=Vincent |date=2019-12-20 |title=Relaxed purifying selection in autopolyploids drives transposable element over-accumulation which provides variants for local adaptation |url=https://www.nature.com/articles/s41467-019-13730-0 |journal=Nature Communications |language=en |volume=10 |issue=1 |pages=5818 |doi=10.1038/s41467-019-13730-0 |pmid=31862875 |bibcode=2019NatCo..10.5818B |s2cid=209420359 |issn=2041-1723|doi-access=free |pmc=6925279 }}</ref>
+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-2011">{{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 | doi-access=free | bibcode=2011JEcol..99.1108P }}</ref> Polyploidy may be associated with increased vigor and adaptability.<ref name="Gilbert-2011">{{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 |doi-access=free }}</ref> However, polyploidization is associated with an increase in [[transposable element]] content<ref>{{Cite journal |last=McClintock |first=B. |date=1984-11-16 |title=The significance of responses of the genome to challenge |url=https://pubmed.ncbi.nlm.nih.gov/15739260/ |journal=Science |volume=226 |issue=4676 |pages=792–801 |doi=10.1126/science.15739260 |issn=0036-8075 |pmid=15739260|bibcode=1984Sci...226..792M }}</ref><ref>{{Cite journal |last1=Matzke |first1=M.A |last2=Matzke |first2=A.J.M |date=June 1998 |title=Polyploidy and transposons |url=https://doi.org/10.1016/S0169-5347(98)01390-1 |journal=Trends in Ecology & Evolution |volume=13 |issue=6 |pages=241 |doi=10.1016/s0169-5347(98)01390-1 |pmid=21238281 |bibcode=1998TEcoE..13R.241M |issn=0169-5347}}</ref> and relaxed [[purifying selection]] on [[recessive]] deleterious alleles.<ref>{{Cite journal |last=Ronfort |first=J. |date=August 1999 |title=The mutation load under tetrasomic inheritance and its consequences for the evolution of the selfing rate in autotetraploid species |journal=Genetics Research |language=en |volume=74 |issue=1 |pages=31–42 |doi=10.1017/S0016672399003845 |issn=1469-5073|doi-access=free }}</ref><ref>{{Cite journal |last1=Baduel |first1=Pierre |last2=Quadrana |first2=Leandro |last3=Hunter |first3=Ben |last4=Bomblies |first4=Kirsten |last5=Colot |first5=Vincent |date=2019-12-20 |title=Relaxed purifying selection in autopolyploids drives transposable element over-accumulation which provides variants for local adaptation |journal=Nature Communications |language=en |volume=10 |issue=1 |pages=5818 |doi=10.1038/s41467-019-13730-0 |pmid=31862875 |bibcode=2019NatCo..10.5818B |s2cid=209420359 |issn=2041-1723|doi-access=free |pmc=6925279 }}</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]].{{citation needed|date=May 2023}}
-In [[unicellular organism]]s the [[ploidy nutrient limitation hypothesis]] suggests that [[nutrient limitation]] should encourage haploidy in preference to higher ploidies. This hypothesis is due to the higher [[surface-to-volume ratio]] of haploids, which eases nutrient uptake, thereby increasing the internal nutrient-to-demand ratio. Mable 2001 finds ''[[Saccharomyces cerevisiae]]'' to be somewhat inconsistent with this hypothesis however, as haploid growth is faster than diploid under high nutrient conditions. The NLH is also tested in haploid, diploid, and polyploid fungi by Gerstein et al 2017. This result is also more complex: On the one hand, under [[phosphorus]] and other nutrient limitation, lower ploidy is selected as expected. However under normal nutrient levels or under limitation of only [[nitrogen]], higher ploidy was selected. Thus the NLH {{endash}} and more generally, the idea that haploidy is selected by harsher conditions {{endash}} is cast into doubt by these results.<ref name="Blischak-et-al-2018">{{cite journal | last1=Blischak | first1=Paul D. | last2=Mabry | first2=Makenzie E. | last3=Conant | first3=Gavin C. | last4=Pires | first4=J. Chris | title=Integrating Networks, Phylogenomics, and Population Genomics for the Study of Polyploidy | journal=[[Annual Review of Ecology, Evolution, and Systematics]] | publisher=[[Annual Reviews (publisher)|Annual Reviews]] | volume=49 | issue=1 | date=2018-11-02 | issn=1543-592X | doi=10.1146/annurev-ecolsys-121415-032302 | pages=253–278| s2cid=92205236 | doi-access=free }}</ref>
+In [[unicellular organism]]s the [[ploidy nutrient limitation hypothesis]] suggests that [[nutrient limitation]] should encourage haploidy in preference to higher ploidies. This hypothesis is due to the higher [[surface-to-volume ratio]] of haploids, which eases nutrient uptake, thereby increasing the internal nutrient-to-demand ratio. Mable 2001 finds ''[[Saccharomyces cerevisiae]]'' to be somewhat inconsistent with this hypothesis however, as haploid growth is faster than diploid under high nutrient conditions. The NLH is also tested in haploid, diploid, and polyploid fungi by Gerstein et al. 2017. This result is also more complex: On the one hand, under [[phosphorus]] and other nutrient limitation, lower ploidy is selected as expected. However under normal nutrient levels or under limitation of only [[nitrogen]], higher ploidy was selected. Thus the NLH {{endash}} and more generally, the idea that haploidy is selected by harsher conditions {{endash}} is cast into doubt by these results.<ref name="Blischak-2018">{{cite journal | last1=Blischak | first1=Paul D. | last2=Mabry | first2=Makenzie E. | last3=Conant | first3=Gavin C. | last4=Pires | first4=J. Chris | title=Integrating Networks, Phylogenomics, and Population Genomics for the Study of Polyploidy | journal=[[Annual Review of Ecology, Evolution, and Systematics]] | publisher=[[Annual Reviews (publisher)|Annual Reviews]] | volume=49 | issue=1 | date=2018-11-02 | issn=1543-592X | doi=10.1146/annurev-ecolsys-121415-032302 | pages=253–278| s2cid=92205236 | doi-access=free }}</ref>
-Older WGDs have also been investigated. Only as recently as 2015 was the ancient [[whole genome duplication]] in [[Baker's yeast]] proven to be [[allopolyploid]], by Marcet-Houben and Gabaldón 2015. It still remains to be explained why there are not more polyploid events in fungi, and the place of [[neopolyploidy]] and [[mesopolyploidy]] in [[evolution of fungi|fungal history]].<ref name="Blischak-et-al-2018" />
+Older WGDs have also been investigated. Only as recently as 2015 was the ancient [[whole genome duplication]] in [[Baker's yeast]] proven to be [[allopolyploid]], by Marcet-Houben and Gabaldón 2015. It still remains to be explained why there are not more polyploid events in fungi, and the place of [[neopolyploidy]] and [[mesopolyploidy]] in [[evolution of fungi|fungal history]].<ref name="Blischak-2018" />
+==Less efficient natural selection in diploid compared to haploid tissue==
+The concept that those [[gene]]s of an organism that are expressed exclusively in the diploid stage are under less efficient [[natural selection]] than those genes expressed in the [[ploidy|haploid]] stage is referred to as the “masking theory”.<ref name="Cervantes-2023">{{cite journal |vauthors=Cervantes S, Kesälahti R, Kumpula TA, Mattila TM, Helanterä H, Pyhäjärvi T |title=Strong Purifying Selection in Haploid Tissue-Specific Genes of Scots Pine Supports the Masking Theory |journal=Mol Biol Evol |volume=40 |issue=8 |pages= |date=August 2023 |pmid=37565532 |pmc=10457172 |doi=10.1093/molbev/msad183 |url=}}</ref>  Evidence in support of this masking theory has been reported in studies of the single-celled yeast ''[[Saccharomyces cerevisiae]]''.<ref>{{cite journal |vauthors=Gerstein AC, Cleathero LA, Mandegar MA, Otto SP |title=Haploids adapt faster than diploids across a range of environments |journal=J Evol Biol |volume=24 |issue=3 |pages=531–40 |date=March 2011 |pmid=21159002 |doi=10.1111/j.1420-9101.2010.02188.x |url=}}</ref>  In further support of the masking theory, evidence of strong purifying selection in haploid tissue-specific genes has been reported for the plant [[Pinus sylvestris|Scots Pine]].<ref name="Cervantes-2023"/>
 ==Glossary of ploidy numbers==
@@ Line 128: / Line 132: @@
  |}
-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.
+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.{{cn|date=June 2024}}
 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.