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Polyploidy
Polyploidy
Polyploidy
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This image shows haploid (single), diploid (double), triploid (triple), and tetraploid (quadruple) sets of chromosomes. Triploid and tetraploid chromosomes are examples of polyploidy.

Polyploidy is a condition in which the cells of an organism have more than two paired sets of (homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two complete sets of chromosomes, one from each of two parents; each set contains the same number of chromosomes, and the chromosomes are joined in pairs of homologous chromosomes. However, some organisms are polyploid. Polyploidy is especially common in plants. Most eukaryotes have diploid somatic cells, but produce haploid gametes (eggs and sperm) by meiosis. A monoploid has only one set of chromosomes, and the term is usually only applied to cells or organisms that are normally diploid. Males of bees and other Hymenoptera, for example, are monoploid. Unlike animals, plants and multicellular algae have life cycles with two alternating multicellular generations. The gametophyte generation is haploid, and produces gametes by mitosis; the sporophyte generation is diploid and produces spores by meiosis.

Polyploidy is the result of whole-genome duplication during the evolution of species. It may occur due to abnormal cell division, either during mitosis, or more commonly from the failure of chromosomes to separate during meiosis or from the fertilization of an egg by more than one sperm.[1] In addition, it can be induced in plants and cell cultures by some chemicals: the best known is colchicine, which can result in chromosome doubling, though its use may have other less obvious consequences as well. Oryzalin will also double the existing chromosome content.

Among mammals, a high frequency of polyploid cells is found in organs such as the brain, liver, heart, and bone marrow.[2] It also occurs in the somatic cells of other animals, such as goldfish,[3] salmon, and salamanders. It is common among ferns and flowering plants (see Hibiscus rosa-sinensis), including both wild and cultivated species. Wheat, for example, after millennia of hybridization and modification by humans, has strains that are diploid (two sets of chromosomes), tetraploid (four sets of chromosomes) with the common name of durum or macaroni wheat, and hexaploid (six sets of chromosomes) with the common name of bread wheat. Many agriculturally important plants of the genus Brassica are also tetraploids. Sugarcane can have ploidy levels higher than octaploid.[4]

Polyploidization can be a mechanism of sympatric speciation because polyploids are usually unable to interbreed with their diploid ancestors. An example is the plant Erythranthe peregrina. Sequencing confirmed that this species originated from E. × robertsii, a sterile triploid hybrid between E. guttata and E. lutea, both of which have been introduced and naturalised in the United Kingdom. New populations of E. peregrina arose on the Scottish mainland and the Orkney Islands via genome duplication from local populations of E. × robertsii.[5] Because of a rare genetic mutation, E. peregrina is not sterile.[6]

On the other hand, polyploidization can also be a mechanism for a kind of 'reverse speciation',[7] whereby gene flow is enabled following the polyploidy event, even between lineages that previously experienced no gene flow as diploids. This has been detailed at the genomic level in Arabidopsis arenosa and Arabidopsis lyrata.[8] Each of these species experienced independent autopolyploidy events (within-species polyploidy, described below), which then enabled subsequent interspecies gene flow of adaptive alleles, in this case stabilising each young polyploid lineage.[9] Such polyploidy-enabled adaptive introgression may allow polyploids at act as 'allelic sponges', whereby they accumulate cryptic genomic variation that may be recruited upon encountering later environmental challenges.[7]

Terminology

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Types

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"Triploid" redirects here. For the human chromosomal disorder (69 XXX, etc.), see Triploid syndrome.

Organ-specific patterns of endopolyploidy (from 2x to 64x) in the giant ant Dinoponera australis

Polyploid types are labeled according to the number of chromosome sets in the nucleus. The letter x is used to represent the number of chromosomes in a single set:

Classification

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Autopolyploidy

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

Two examples of natural autopolyploids are the piggyback plant, Tolmiea menzisii[19] and the white sturgeon, Acipenser transmontanum.[20] Most instances of autopolyploidy result from the fusion of unreduced (2n) gametes, which results in either triploid (n + 2n = 3n) or tetraploid (2n + 2n = 4n) offspring.[21] Triploid offspring are typically sterile (as in the phenomenon of triploid block), but in some cases they may produce high proportions of unreduced gametes and thus aid the formation of tetraploids. This pathway to tetraploidy is referred to as the triploid bridge.[21] Triploids may also persist through asexual reproduction. In fact, stable autotriploidy in plants is often associated with apomictic mating systems.[22] In agricultural systems, autotriploidy can result in seedlessness, as in watermelons and bananas.[23] Triploidy is also utilized in salmon and trout farming to induce sterility.[24][25]

Rarely, autopolyploids arise from spontaneous, somatic genome doubling, which has been observed in apple (Malus domesticus) bud sports.[26] This is also the most common pathway of artificially induced polyploidy, where methods such as protoplast fusion or treatment with colchicine, oryzalin or mitotic inhibitors are used to disrupt normal mitotic division, which results in the production of polyploid cells. This process can be useful in plant breeding, especially when attempting to introgress germplasm across ploidal levels.[27]

Autopolyploids possess at least three homologous chromosome sets, which can lead to high rates of multivalent pairing during meiosis (particularly in recently formed autopolyploids, also known as neopolyploids) and an associated decrease in fertility due to the production of aneuploid gametes.[28] Natural or artificial selection for fertility can quickly stabilize meiosis in autopolyploids by restoring bivalent pairing during meiosis. Rapid adaptive evolution of the meiotic machinery, resulting in reduced levels of multivalents (and therefore stable autopolyploid meiosis) has been documented in Arabidopsis arenosa[29] and Arabidopsis lyrata,[8] with specific adaptive alleles of these species shared between only the evolved polyploids.[8][30]

The high degree of homology among duplicated chromosomes causes autopolyploids to display polysomic inheritance.[31] This trait is often used as a diagnostic criterion to distinguish autopolyploids from allopolyploids, which commonly display disomic inheritance after they progress past the neopolyploid stage.[32] While most polyploid species are unambiguously characterized as either autopolyploid or allopolyploid, these categories represent the ends of a spectrum of divergence between parental subgenomes. Polyploids that fall between these two extremes, which are often referred to as segmental allopolyploids, may display intermediate levels of polysomic inheritance that vary by locus.[33][34]

About half of all polyploids are thought to be the result of autopolyploidy,[35][36] although many factors make this proportion hard to estimate.[37]

Allopolyploidy

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Allopolyploids or amphipolyploids or heteropolyploids are polyploids with chromosomes derived from two or more diverged taxa.

As in autopolyploidy, this primarily occurs through the fusion of unreduced (2n) gametes, which can take place before or after hybridization. In the former case, unreduced gametes from each diploid taxon – or reduced gametes from two autotetraploid taxa – combine to form allopolyploid offspring. In the latter case, one or more diploid F1 hybrids produce unreduced gametes that fuse to form allopolyploid progeny.[38] Hybridization followed by genome duplication may be a more common path to allopolyploidy because F1 hybrids between taxa often have relatively high rates of unreduced gamete formation – divergence between the genomes of the two taxa result in abnormal pairing between homoeologous chromosomes or nondisjunction during meiosis.[38] In this case, allopolyploidy can actually restore normal, bivalent meiotic pairing by providing each homoeologous chromosome with its own homologue. If divergence between homoeologous chromosomes is even across the two subgenomes, this can theoretically result in rapid restoration of bivalent pairing and disomic inheritance following allopolyploidization. However multivalent pairing is common in many recently formed allopolyploids, so it is likely that the majority of meiotic stabilization occurs gradually through selection.[28][32]

Because pairing between homoeologous chromosomes is rare in established allopolyploids, they may benefit from fixed heterozygosity of homoeologous alleles.[39] In certain cases, such heterozygosity can have beneficial heterotic effects, either in terms of fitness in natural contexts or desirable traits in agricultural contexts. This could partially explain the prevalence of allopolyploidy among crop species. Both bread wheat and triticale are examples of an allopolyploids with six chromosome sets. Cotton, peanut, and quinoa are allotetraploids with multiple origins. In Brassicaceous crops, the Triangle of U describes the relationships between the three common diploid Brassicas (B. oleracea, B. rapa, and B. nigra) and three allotetraploids (B. napus, B. juncea, and B. carinata) derived from hybridization among the diploid species. A similar relationship exists between three diploid species of Tragopogon (T. dubius, T. pratensis, and T. porrifolius) and two allotetraploid species (T. mirus and T. miscellus).[40] Complex patterns of allopolyploid evolution have also been observed in animals, as in the frog genus Xenopus.[41]

Aneuploid

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Main article: Aneuploidy

Organisms in which a particular chromosome, or chromosome segment, is under- or over-represented are said to be aneuploid (from the Greek words meaning "not", "good", and "fold"). Aneuploidy refers to a numerical change in part of the chromosome set, whereas polyploidy refers to a numerical change in the whole set of chromosomes.[42]

Endopolyploidy

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Polyploidy occurs in some tissues of animals that are otherwise diploid, such as human muscle tissues.[43] This is known as endopolyploidy. Species whose cells do not have nuclei, that is, prokaryotes, may be polyploid, as seen in the large bacterium Epulopiscium fishelsoni.[44] Hence ploidy is defined with respect to a cell.

Monoploid

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Main article: Monoploidy

A monoploid has only one set of chromosomes and the term is usually only applied to cells or organisms that are normally diploid. The more general term for such organisms is haploid.

Temporal terms

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Neopolyploidy

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A polyploid that is newly formed.

Mesopolyploidy

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That has become polyploid in more recent history; it is not as new as a neopolyploid and not as old as a paleopolyploid. It is a middle aged polyploid. Often this refers to whole genome duplication followed by intermediate levels of diploidization.

Paleopolyploidy

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This phylogenetic tree shows the relationship between the best-documented instances of paleopolyploidy in eukaryotes.
Main article: Paleopolyploidy

Ancient genome duplications probably occurred in the evolutionary history of all life. Duplication events that occurred long ago in the history of various evolutionary lineages can be difficult to detect because of subsequent diploidization (such that a polyploid starts to behave cytogenetically as a diploid over time) as mutations and gene translations gradually make one copy of each chromosome unlike the other copy. Over time, it is also common for duplicated copies of genes to accumulate mutations and become inactive pseudogenes.[45]

In many cases, these events can be inferred only through comparing sequenced genomes. Examples of unexpected but recently confirmed ancient genome duplications include baker's yeast (Saccharomyces cerevisiae), mustard weed/thale cress (Arabidopsis thaliana), rice (Oryza sativa), and two rounds of whole genome duplication (the 2R hypothesis) in an early evolutionary ancestor of the vertebrates (which includes the human lineage) and another near the origin of the teleost fishes.[46] Angiosperms (flowering plants) have paleopolyploidy in their ancestry. All eukaryotes probably have experienced a polyploidy event at some point in their evolutionary history.

Other similar terms

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Karyotype

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Main article: Karyotype

A karyotype is the characteristic chromosome complement of a eukaryote species.[47][48] The preparation and study of karyotypes is part of cytology and, more specifically, cytogenetics.

Although the replication and transcription of DNA is highly standardized in eukaryotes, the same cannot be said for their karyotypes, which are highly variable between species in chromosome number and in detailed organization despite being constructed out of the same macromolecules. In some cases, there is even significant variation within species. This variation provides the basis for a range of studies in what might be called evolutionary cytology.

Homoeologous chromosomes

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Main article: Homoeology

Homoeologous chromosomes are those brought together following inter-species hybridization and allopolyploidization, and whose relationship was completely homologous in an ancestral species. For example, durum wheat is the result of the inter-species hybridization of two diploid grass species Triticum urartu and Aegilops speltoides. Both diploid ancestors had two sets of 7 chromosomes, which were similar in terms of size and genes contained on them. Durum wheat contains a hybrid genome with two sets of chromosomes derived from Triticum urartu and two sets of chromosomes derived from Aegilops speltoides. Each chromosome pair derived from the Triticum urartu parent is homoeologous to the opposite chromosome pair derived from the Aegilops speltoides parent, though each chromosome pair unto itself is homologous.

Examples

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Humans

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Schematic karyogram of a human, showing the normal diploid (that is, non-polyploid) karyotype. It shows 22 homologous chromosomes, both the female (XX) and male (XY) versions of the sex chromosome (bottom right), as well as the mitochondrial genome (to scale at bottom left).
Further information: Karyotype
Further information: Triploid syndrome

True polyploidy rarely occurs in humans, although polyploid cells occur in highly differentiated tissue, such as liver parenchyma, heart muscle, placenta and in bone marrow.[49][50] Aneuploidy is more common.

Polyploidy occurs in humans in the form of triploidy, with 69 chromosomes (sometimes called 69, XXX), and tetraploidy with 92 chromosomes (sometimes called 92, XXXX). Triploidy, usually due to polyspermy, occurs in about 2–3% of all human pregnancies and ~15% of miscarriages.[citation needed] The vast majority of triploid conceptions end as a miscarriage; those that do survive to term typically die shortly after birth. In some cases, survival past birth may be extended if there is mixoploidy with both a diploid and a triploid cell population present. There has been one report of a child surviving to the age of seven months with complete triploidy syndrome. He failed to exhibit normal mental or physical neonatal development, and died from a Pneumocystis carinii infection, which indicates a weak immune system.[51]

Triploidy may be the result of either digyny (the extra haploid set is from the mother) or diandry (the extra haploid set is from the father). Diandry is mostly caused by reduplication of the paternal haploid set from a single sperm, but may also be the consequence of dispermic (two sperm) fertilization of the egg.[52] Digyny is most commonly caused by either failure of one meiotic division during oogenesis leading to a diploid oocyte or failure to extrude one polar body from the oocyte. Diandry appears to predominate among early miscarriages, while digyny predominates among triploid zygotes that survive into the fetal period.[53] However, among early miscarriages, digyny is also more common in those cases less than 8+1⁄2 weeks gestational age or those in which an embryo is present. There are also two distinct phenotypes in triploid placentas and fetuses that are dependent on the origin of the extra haploid set. In digyny, there is typically an asymmetric poorly grown fetus, with marked adrenal hypoplasia and a very small placenta.[54] In diandry, a partial hydatidiform mole develops.[52] These parent-of-origin effects reflect the effects of genomic imprinting.[citation needed]

Complete tetraploidy is more rarely diagnosed than triploidy, but is observed in 1–2% of early miscarriages. However, some tetraploid cells are commonly found in chromosome analysis at prenatal diagnosis and these are generally considered 'harmless'. It is not clear whether these tetraploid cells simply tend to arise during in vitro cell culture or whether they are also present in placental cells in vivo. There are, at any rate, very few clinical reports of fetuses/infants diagnosed with tetraploidy mosaicism.

Mixoploidy is quite commonly observed in human preimplantation embryos and includes haploid/diploid as well as diploid/tetraploid mixed cell populations. It is unknown whether these embryos fail to implant and are therefore rarely detected in ongoing pregnancies or if there is simply a selective process favoring the diploid cells.

Other animals

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Examples in animals are more common in non-vertebrates[55] such as flatworms, leeches, and brine shrimp. Polyploidy also occurs commonly in amphibians; for example the biomedically important genus Xenopus contains many different species with as many as 12 sets of chromosomes (dodecaploid).[56] Polyploid lizards are also quite common. Most are sterile and reproduce by parthenogenesis;[citation needed] others, like Liolaemus chiliensis, maintain sexual reproduction. Polyploid mole salamanders (mostly triploids) are all female and reproduce by kleptogenesis,[57] "stealing" spermatophores from diploid males of related species to trigger egg development but not incorporating the males' DNA into the offspring.

While some tissues of mammals, such as parenchymal liver cells, are polyploid,[58][59] rare instances of polyploid mammals are known, but most often result in prenatal death. An octodontid rodent of Argentina's harsh desert regions, known as the plains viscacha rat (Tympanoctomys barrerae) has been reported as an exception to this 'rule'.[60] However, careful analysis using chromosome paints shows that there are only two copies of each chromosome in T. barrerae, not the four expected if it were truly a tetraploid.[61] This rodent is not a rat, but kin to guinea pigs and chinchillas. Its "new" diploid (2n) number is 102 and so its cells are roughly twice normal size. Its closest living relation is Octomys mimax, the Andean Viscacha-Rat of the same family, whose 2n = 56. It was therefore surmised that an Octomys-like ancestor produced tetraploid (i.e., 2n = 4x = 112) offspring that were, by virtue of their doubled chromosomes, reproductively isolated from their parents.

Polyploidy was induced in fish by Har Swarup (1956) using a cold-shock treatment of the eggs close to the time of fertilization, which produced triploid embryos that successfully matured.[62][63] Cold or heat shock has also been shown to result in unreduced amphibian gametes, though this occurs more commonly in eggs than in sperm.[64] John Gurdon (1958) transplanted intact nuclei from somatic cells to produce diploid eggs in the frog, Xenopus (an extension of the work of Briggs and King in 1952) that were able to develop to the tadpole stage.[65] The British scientist J. B. S. Haldane hailed the work for its potential medical applications and, in describing the results, became one of the first to use the word "clone" in reference to animals. Later work by Shinya Yamanaka showed how mature cells can be reprogrammed to become pluripotent, extending the possibilities to non-stem cells. Gurdon and Yamanaka were jointly awarded the Nobel Prize in 2012 for this work.[65]

Fish

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A polyploidy event occurred within the stem lineage of the teleost fish.[46] Some fish which include the salmonids and many cyprinids (i.e. carp) exhibit stable polyploidy, where entire species consist entirely of polyploid individuals. Some fish[examples needed] have as many as 400 chromosomes.[66]

Plants

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Speciation via polyploidy: A diploid cell undergoes failed meiosis, producing diploid gametes, which self-fertilize to produce a tetraploid zygote.

Polyploidy is frequent in plants, some estimates suggesting that 30–80% of living plant species are polyploid, and many lineages show evidence of ancient polyploidy (paleopolyploidy) in their genomes.[67][68][69][70] Huge explosions in angiosperm species diversity appear to have coincided with the timing of ancient genome duplications shared by many species.[71] It has been established that 15% of angiosperm and 31% of fern speciation events are accompanied by ploidy increase.[72]

Polyploid plants can arise spontaneously in nature by several mechanisms, including meiotic or mitotic failures, and fusion of unreduced (2n) gametes.[39] Both autopolyploids (e.g. potato[73]) and allopolyploids (such as canola, wheat and cotton) can be found among both wild and domesticated plant species.

Most polyploids display novel variation or morphologies relative to their parental species, that may contribute to the processes of speciation and eco-niche exploitation.[68][39] The mechanisms leading to novel variation in newly formed allopolyploids may include gene dosage effects (resulting from more numerous copies of genome content), the reunion of divergent gene regulatory hierarchies, chromosomal rearrangements, and epigenetic remodeling, all of which affect gene content and/or expression levels.[74][75][76][77] Many of these rapid changes may contribute to reproductive isolation and speciation. However, seed generated from interploidy crosses, such as between polyploids and their parent species, usually have aberrant endosperm development which impairs their viability,[78][79] thus contributing to polyploid speciation. Polyploids may also interbreed with diploids and produce polyploid seeds, as observed in the agamic complexes of Crepis.[80]

Some plants are triploid. As meiosis is disturbed, these plants are sterile, with all plants having the same genetic constitution: Among them, the exclusively vegetatively propagated saffron crocus (Crocus sativus). Also, the extremely rare Tasmanian shrub Lomatia tasmanica is a triploid sterile species.

There are few naturally occurring polyploid conifers.[81] One example is the Coast Redwood Sequoia sempervirens, which is a hexaploid (6x) with 66 chromosomes (2n = 6x = 66), although the origin is unclear.[82]

Aquatic plants, especially the Monocotyledons, include a large number of polyploids.[83]

Crops

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The induction of polyploidy is a common technique to overcome the sterility of a hybrid species during plant breeding. For example, triticale is the hybrid of wheat (Triticum turgidum) and rye (Secale cereale). It combines sought-after characteristics of the parents, but the initial hybrids are sterile. After polyploidization, the hybrid becomes fertile and can thus be further propagated to become triticale.

In some situations, polyploid crops are preferred because they are sterile. For example, many seedless fruit varieties are seedless as a result of polyploidy. Such crops are propagated using asexual techniques, such as grafting.

Polyploidy in crop plants is most commonly induced by treating seeds with the chemical colchicine.

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

Fungi

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Besides plants and animals, the evolutionary history of various fungal species is dotted by past and recent whole-genome duplication events (see Albertin and Marullo 2012[87] for review). Several examples of polyploids are known:

In addition, polyploidy is frequently associated with hybridization and reticulate evolution that appear to be highly prevalent in several fungal taxa. Indeed, homoploid speciation (hybrid speciation without a change in chromosome number) has been evidenced for some fungal species (such as the basidiomycota Microbotryum violaceum[95]).

Schematic phylogeny of the Chromalveolata. Red circles indicate polyploidy, blue squares indicate hybridization. From Albertin and Marullo, 2012[87]

As for plants and animals, fungal hybrids and polyploids display structural and functional modifications compared to their progenitors and diploid counterparts. In particular, the structural and functional outcomes of polyploid Saccharomyces genomes strikingly reflect the evolutionary fate of plant polyploid ones. Large chromosomal rearrangements[96] leading to chimeric chromosomes[97] have been described, as well as more punctual genetic modifications such as gene loss.[98] The homoealleles of the allotetraploid yeast S. pastorianus show unequal contribution to the transcriptome.[99] Phenotypic diversification is also observed following polyploidization and/or hybridization in fungi,[100] producing the fuel for natural selection and subsequent adaptation and speciation.

Chromalveolata

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Other eukaryotic taxa have experienced one or more polyploidization events during their evolutionary history (see Albertin and Marullo, 2012[87] for review). The oomycetes, which are non-true fungi members, contain several examples of paleopolyploid and polyploid species, such as within the genus Phytophthora.[101] Some species of brown algae (Fucales, Laminariales[102] and diatoms[103]) contain apparent polyploid genomes. In the Alveolata group, the remarkable species Paramecium tetraurelia underwent three successive rounds of whole-genome duplication[104] and established itself as a major model for paleopolyploid studies.

Bacteria

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Each Deinococcus radiodurans bacterium contains 4-8 copies of its chromosome.[105] Exposure of D. radiodurans to X-ray irradiation or desiccation can shatter its genomes into hundred of short random fragments. Nevertheless, D. radiodurans is highly resistant to such exposures. The mechanism by which the genome is accurately restored involves RecA-mediated homologous recombination and a process referred to as extended synthesis-dependent strand annealing (SDSA).[106]

Azotobacter vinelandii can contain up to 80 chromosome copies per cell.[107] However this is only observed in fast growing cultures, whereas cultures grown in synthetic minimal media are not polyploid.[108]

Archaea

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The archaeon Halobacterium salinarium is polyploid[109] and, like Deinococcus radiodurans, is highly resistant to X-ray irradiation and desiccation, conditions that induce DNA double-strand breaks.[110] Although chromosomes are shattered into many fragments, complete chromosomes can be regenerated by making use of overlapping fragments. The mechanism employs single-stranded DNA binding protein and is likely homologous recombinational repair.[111]

See also

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References

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Further reading

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Polyploidy

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Polyploidy is the heritable condition in which an organism or cell possesses more than two complete sets of chromosomes in its , resulting from whole-genome duplication events. This phenomenon is widespread among plants, occurring in an estimated 30–80% of angiosperm depending on the lineage, and is less common but present in certain , fungi, and animals such as amphibians and . Polyploidy plays a pivotal in by promoting , , and to environmental stresses through mechanisms like altered and increased cell size. There are two primary types of polyploidy: autopolyploidy and allopolyploidy. Autopolyploidy arises within a single via doubling, often due to errors in or that produce unreduced gametes, leading to organisms with multiple identical sets. In contrast, allopolyploidy occurs through interspecific hybridization followed by duplication, combining divergent sets from different and frequently resulting in immediate . Segmental allopolyploids represent an intermediate form where partial homology exists between , blending characteristics of both types. The evolutionary significance of polyploidy is profound, particularly in , where ancient whole-genome duplications have contributed to the diversification of major lineages, including all angiosperms. These events enable sub- or neofunctionalization of duplicated genes, fostering novel traits such as enhanced stress tolerance and larger organs, which can confer ecological advantages in changing environments. In animals, polyploidy is rarer due to stricter dosage compensation requirements but has facilitated adaptations in groups like salmonids and parthenogenetic . Overall, polyploidy acts as both a driver of and a potential source of genomic instability, influencing from cellular to levels.

Fundamentals

Definition

Polyploidy is the condition in which the cells of an contain more than two complete sets of chromosomes, resulting from whole-genome duplication events. In most eukaryotic species, the typical state is diploid (2n), with two homologous sets of chromosomes derived from the haploid (n) gametes; polyploid organisms, by contrast, possess three or more such sets, such as triploid (3n) or tetraploid (4n) configurations. This phenomenon is particularly prevalent in , where it contributes significantly to and . The first documented observation of polyploidy occurred in 1907, when botanist Anne M. Lutz identified the evening primrose variant Oenothera gigas—initially noted by Hugo de Vries in 1905—as possessing double the chromosome number of its diploid progenitor O. lamarckiana. Polyploidy represents a specific form of euploidy, defined as having a chromosome complement that is an exact multiple of the haploid set, in distinction to aneuploidy, which involves the gain or loss of one or more individual chromosomes, leading to imbalanced genomic content. Polyploidy commonly induces larger cell sizes, a termed the "gigas effect," due to increased genomic content influencing cellular volume and organelle scaling. It also alters patterns through mechanisms like dosage compensation and regulatory network rewiring, potentially enhancing phenotypic novelty or stress tolerance. Regarding reproduction, even-ploidy levels (e.g., 4n) often permit balanced and fertility, whereas odd-ploidy states (e.g., 3n) typically cause sterility from unequal and segregation.

Ploidy Levels

Ploidy levels refer to the number of complete sets of in a , building on the concept of as the condition of having more than two such sets. The standard notation uses "n" to denote the haploid (monoploid) number of , representing one complete set; thus, a diploid has 2n , a triploid has 3n, and so on for higher multiples. In polyploid contexts, "x" is often used to indicate the basic number of the ancestral , allowing description of as multiples like 2x for diploid or for tetraploid, which helps distinguish the underlying genomic structure. Monoploidy, denoted as n or 1x, serves as the baseline with a single set and occurs rarely in due to its and reduced genetic redundancy, though it is valuable in for and rapid fixation of traits. Among common polyploid levels, triploidy (3n) frequently results in sterility because the odd number of sets prevents even pairing during , leading to unbalanced gametes. In contrast, tetraploidy (4n) typically supports , particularly in , as the even enables pairing and regular segregation in I. Higher even levels, such as hexaploidy (6n) and octoploidy (8n), are also prevalent in certain lineages and generally permit reproductive viability through multivalent or bivalent formations during . Overall, even levels facilitate balanced distribution and , while odd levels disrupt meiotic processes, often rendering organisms sterile.

Classification

Autopolyploidy

Autopolyploidy arises from the multiplication of sets within a single , resulting in organisms that possess more than two complete sets of derived from the same . This form of polyploidy contrasts with allopolyploidy by involving no interspecies hybridization, instead relying on intragenomic duplication events that increase levels, such as from diploid (2n) to tetraploid (4n). Taxonomically, autopolyploids are defined by the presence of multiple identical or nearly identical genomes within an individual or , often leading to polysomic where alleles segregate among more than two homologous . The formation of autopolyploids typically occurs through natural or induced mechanisms that disrupt normal segregation. In nature, common processes include the production of unreduced gametes via meiotic , where all fail to separate properly and move into one daughter cell, or somatic doubling during when is not followed by . Artificially, autopolyploidy is frequently induced using , an that binds to and inhibits spindle fiber formation, thereby preventing alignment and separation during . These methods have been instrumental in creating polyploid varieties for agriculture, with treatments applied to meristematic tissues to generate stable polyploid lines. A key cytological feature of autopolyploids is the potential for multivalent pairing during meiosis, where homologous chromosomes from the duplicated sets form complex structures like trivalents or quadrivalents rather than simple bivalents. This multivalent configuration arises because all chromosome copies are highly similar, allowing preferential pairing among more than two homologs, which can complicate chromosome segregation and lead to irregular gamete formation. Autopolyploids often exhibit the gigas effect, a nucleotypic response to increased DNA content that enlarges cell size, stomatal guard cells, and overall organ dimensions, contributing to greater biomass and vigor in many cases.01132-5) Prominent examples of autopolyploids include the cultivated (Musa acuminata), a triploid (3n) form derived from chromosome doubling in its diploid , which is propagated vegetatively to maintain sterility and seedlessness. Similarly, the (Solanum tuberosum), a staple , exists as a tetraploid (4n) autopolyploid originating from South American wild diploids through unreduced formation, enhancing size and yield. These cases illustrate how autopolyploidy has been fixed in crops via or selection for fertility. While autopolyploidy provides advantages such as enhanced heterozygosity, effects that boost metabolic capacity, and increased environmental resilience through the gigas effect, it also presents challenges including meiotic instability. Multivalent pairings frequently result in unbalanced distribution, producing aneuploid gametes and reduced , particularly in odd-ploidy levels like triploids. Despite these drawbacks, many autopolyploids achieve stability over generations through selection for bivalent pairing or diploidization-like processes, enabling their persistence in natural and cultivated populations.

Allopolyploidy

Allopolyploidy refers to a form of polyploidy in which the possesses two or more complete sets of chromosomes derived from different , typically resulting from interspecific hybridization followed by whole-genome duplication. Unlike autopolyploidy, which involves duplication within a single , allopolyploidy combines divergent genomes, leading to a new with a composite nuclear structure. The formation of allopolyploids begins with hybridization between individuals of distinct , producing a sterile due to mismatched that fail to pair properly during . This sterility is often resolved through chromosome doubling, either somatically or via unreduced gametes, which restores fertility by creating pairs of homologous chromosomes from each parental , known as homoeologues. For instance, a tetraploid allopolyploid can arise from the union of two diploid when the hybrid undergoes genome duplication, effectively doubling each contributed and enabling bivalent formation. A key characteristic of allopolyploids is the presence of homoeologous chromosomes—similar but not identical copies from different ancestral —that generally exhibit preferential pairing during , favoring interactions between chromosomes from the same subgenome over random multivalent associations. This preferential pairing promotes diploid-like meiotic behavior and inheritance patterns, despite the higher level, which stabilizes the and reduces risks. As a result, allopolyploids often display disomic inheritance for most loci, mimicking diploid segregation ratios. Prominent examples include bread wheat (Triticum aestivum), an allohexaploid (2n = 6x = 42) formed through successive hybridizations and duplications involving three diploid progenitor : Triticum urartu (A ), an unidentified Aegilops (B ), and Aegilops tauschii (D ). Similarly, upland cotton (Gossypium hirsutum) is an allotetraploid resulting from hybridization between an A-genome diploid (African origin) and a D-genome diploid (American origin) approximately 1–2 million years ago, followed by doubling. Genetically, allopolyploidy induces subgenome dominance, where one parental subgenome may express more genes or exhibit higher activity than the other, influencing traits like seed storage protein accumulation in cotton. This process often involves gene silencing, loss, or activation, as seen in newly synthesized wheat allotetraploids where up to 15% of genes show non-additive expression changes shortly after formation. Such alterations contribute to instant speciation by establishing reproductive isolation from parental species through chromosomal incompatibility and novel gene regulation, enabling rapid evolutionary innovation.

Temporal Aspects

Neopolyploidy

Neopolyploidy refers to polyploids that have arisen in recent evolutionary time, generally within the last few thousand years or more recently, such as in the past few centuries, and are identifiable through ongoing genomic and gene evolution processes. These formations typically result from mechanisms like whole-genome duplication or hybridization followed by genome doubling, leading to organisms with multiple chromosome sets that retain high structural and sequence integrity. Unlike more ancient polyploids, neopolyploids exhibit active evolutionary changes, making them valuable models for studying the immediate aftermath of polyploid formation. Key characteristics of neopolyploids include high sequence similarity among duplicated s, reflecting their youth, and an ongoing process of diploidization where genetic redundancy is reduced through mechanisms such as loss, subfunctionalization, or silencing of homeologous copies. This diploidization helps resolve meiotic instabilities but can also drive rapid genomic restructuring, including chromosomal rearrangements and epigenetic modifications. For instance, in neopolyploids, duplicated loci often show biased patterns that evolve quickly to restore balanced regulation. Prominent examples illustrate these traits in plants. Spartina anglica, an invasive allotetraploid cordgrass, formed around 150 years ago in via hybridization between the diploid Spartina maritima and the introduced hexaploid Spartina alterniflora, followed by doubling to yield 2n ≈ 120 chromosomes. This neopolyploid has since spread widely, demonstrating vigorous growth and colonization. Similarly, in the Tragopogon, the allotetraploids T. mirus and T. miscellus emerged approximately 80 years ago in the from interspecific hybrids of introduced diploid species (T. dubius, T. pratensis, and T. porrifolius), with multiple independent origins documented. These cases highlight recurrent neopolyploid in settings. Detection of neopolyploids relies on molecular clocks, which estimate formation age from low rates between homeologs, and synteny analysis, which confirms minimal divergence in gene order and content across duplicated regions. In Tragopogon polyploids, for example, cytogenetic mapping reveals near-collinear homeologous chromosomes with few rearrangements since formation. Evolutionarily, neopolyploids enable rapid adaptation through enhanced genetic and , allowing exploitation of novel niches like disturbed habitats, but they often face elevated risks due to meiotic challenges, reduced in early generations, and lower fitness in benign environments compared to diploids. Studies indicate that while some, like Spartina anglica, achieve ecological success, many neopolyploid lineages fail to persist long-term, underscoring their dynamic but precarious role in .

Paleopolyploidy

Paleopolyploidy refers to ancient whole-genome duplication (WGD) events that occurred more than 10 to 100 million years ago, often predating the diversification of major lineages and leaving detectable traces in contemporary genomes through duplicated genes known as ohnologs. These events are distinguished from more recent neopolyploidy by their deep evolutionary age, with genomic signatures shaped by extensive diploidization processes over millions of years. Key characteristics of paleopolyploidy include progressive diploidization, where redundant chromosomes and genes are lost or rearranged, leading to a return to a near-diploid state punctuated by periods of genomic stability and rapid evolutionary change. This involves widespread loss, with up to 80% of duplicated genes eliminated, alongside chromosomal rearrangements that disrupt original synteny and create mosaic genomes. Such dynamics result in punctuated equilibria, where bursts of duplication foster innovation followed by refinement through selection. In model organisms, these traces manifest as large blocks of collinear duplicated segments covering significant portions of the , such as one-third in . Inference of paleopolyploidy relies on identifying patterns of genomic colinearity, where paralogous genes maintain order across chromosomes, and analyzing peaks in the distribution of Ks values—the number of synonymous substitutions per synonymous site—among paralogous gene pairs, which indicate the timing of ancient duplications. For instance, secondary peaks in Ks histograms, distinct from background tandem duplications, signal WGD events when aligned with phylogenetic divergence times. Prominent examples include multiple ancient WGDs in the model plant , with events dated to approximately 35 million years ago (α duplication) and older ones around 90–100 million years ago (β) and further back for the γ event, inferred from phylogenetic analysis of chromosomal duplication events across angiosperms. Similarly, the yeast experienced a WGD roughly 100 million years ago, post-divergence from other yeasts, evidenced by widespread duplicated chromosomal segments and expanded families. In vertebrates, the 2R hypothesis posits two rounds of paleopolyploidy near the chordate-vertebrate transition around 500 million years ago, supported by ohnolog clusters and syntenic blocks that underpin the evolution of complex traits like the . These ancient events have profoundly influenced eukaryotic by providing raw genetic material for diversification, underpinning major radiations such as the angiosperm and complexity through enhanced repertoire and regulatory flexibility.

Mechanisms of Formation

Genomic Duplication Processes

Genomic duplication processes represent intrinsic cellular errors or induced disruptions that lead to the replication of entire sets without corresponding , resulting in polyploid cells or organisms primarily through autopolyploidy. These mechanisms occur independently of intergenomic hybridization and are pivotal in both natural and experimental contexts for generating polyploidy. In nature, such duplications arise sporadically but can be amplified under environmental stress, while artificial induction relies on chemical agents to mimic or enhance these errors. Somatic mechanisms of genomic duplication primarily involve , a modified where proceeds without subsequent or , yielding polytene or polyploid nuclei with multiple copies. Endoreduplication is widespread across eukaryotes, facilitating cell enlargement and differentiation in tissues such as plant endosperm or animal secretory glands, and it can propagate to form polyploid organs or whole organisms if occurring in meristematic cells. Closely related is endomitosis, where chromosomes replicate but fail to segregate due to spindle dysfunction, similarly producing polyploid cells; these processes often overlap in terminology but share the outcome of somatic genome doubling without involvement. In pathological contexts, endoreduplication contributes to tumor polyploidy in animals, where polyploid giant cancer cells emerge via repeated replication cycles, enhancing resistance to and promoting tumor heterogeneity and progression. Gametic mechanisms generate unreduced (2n) gametes through meiotic restitution, where reduction fails, preserving the somatic number for transmission to . First-division restitution (FDR) occurs when homologous fail to segregate during I, resulting in dyads with unreduced that form balanced 2n gametes upon . Second-division restitution (SDR), in contrast, involves normal I but aberrant II, leading to restitution nuclei that produce 2n gametes with potential heterozygote deficiencies. These restitution events stem from spindle irregularities, premature , or omission, and their fusion—either 2n with 2n (bilateral) or 2n with n (unilateral)—directly yields polyploid zygotes. Chemical induction of polyploidy exploits mitotic spindle poisons like , an that binds and prevents , thereby inhibiting segregation during and causing cells to exit with duplicated . This results in immediate doubling of the in treated tissues, often applied to seedlings or explants to produce polyploids after regeneration. Colchicine's efficacy varies by concentration and exposure duration, with typical rates inducing 10-50% polyploidy in responsive species, though it carries risks of and chimeric outcomes. In natural settings, genomic duplication via unreduced gametes is infrequent, typically ranging from 0.1% to 10% in wild populations, but frequencies can surge to over 30% under abiotic stresses like extremes or , which disrupt meiotic fidelity. Somatic duplications are more common in specific developmental contexts but rarely lead to heritable polyploidy without gametic involvement. Overall, these processes yield immediate polyploid tissues, organs, or viable organisms, with autopolyploid outcomes dominating, and in animals, they underpin pathological polyploidy in tumors that drives through genomic .

Hybridization Events

Hybridization events play a central role in the formation of allopolyploids, where interspecific crosses between partially compatible generate hybrid offspring that subsequently undergo chromosome doubling to achieve reproductive stability. These crosses typically occur between species with divergent genomes, resulting in F1 hybrids that possess one set of chromosomes from each parent. Due to genetic differences, homologous chromosomes fail to pair properly during , leading to unbalanced gametes and sterility in these hybrids. This meiotic instability arises from the lack of pairing partners, causing chromosome segregation errors and inviable spores. Chromosome doubling in these sterile F1 hybrids, often triggered spontaneously through mechanisms like the failure of or induced by environmental stresses or chemical agents such as , restores fertility by creating a duplicated where each now has a homologous counterpart from the same parental origin. This process transforms the diploid hybrid into a fertile amphidiploid, enabling bivalent pairing during and the production of balanced gametes. By resolving genomic incompatibilities, such as mismatched functions or regulatory imbalances that initially hinder hybrid viability, doubling allows the combined parental genomes to function cohesively, often resulting in enhanced vigor or novel adaptations. Hybridization events can be classified as bilateral (reciprocal crosses where both directions are viable) or unilateral (one-directional crosses due to asymmetric incompatibilities, such as growth barriers in one parent). Bilateral hybrids facilitate more symmetric gene contributions, while unilateral ones may limit but still lead to polyploids if doubling occurs. Polyploid bridge species, such as intermediate polyploids, can further mediate these events by enabling between otherwise isolated diploids through , as seen in systems where triploid hybrids act as intermediaries. Examples include the formation of the invasive hexaploid anglica around 1870 in European salt marshes, arising from the unilateral hybridization of the introduced tetraploid S. alterniflora and native diploid S. maritima, yielding a sterile triploid hybrid (S. × townsendii) that doubled to form the fertile allopolyploid. Similarly, the allotetraploids Tragopogon mirus and T. miscellus originated multiple times in the early 20th century in via bilateral hybridization between introduced diploids T. dubius and T. porrifolius, followed by spontaneous doubling in hybrid zones. These events frequently occur in hybrid zones—geographic areas of where parental species overlap and interbreed—fostering polyploid formation through increased hybridization opportunities. Such zones, often in disturbed or marginal habitats like roadsides or coastal regions altered by human activity, provide selective pressures that favor polyploid establishment by reducing and enhancing hybrid survival. In , disturbed agricultural fields in the served as crucibles for repeated polyploid origins, accelerating lineage divergence by instantly creating reproductively isolated entities. Overall, hybridization-driven polyploidy exemplifies a rapid mechanism, particularly prevalent in where it has contributed to the diversification of genera like and .

Biological Occurrence

In Plants

Polyploidy is particularly prevalent in , where it has played a significant role in their evolutionary diversification and adaptation. Estimates indicate that 30–70% of angiosperm species are polyploid, reflecting a high incidence of whole-genome duplications throughout their . This prevalence is even higher in ferns, with up to 95% of species exhibiting polyploidy at some point in their lineage. The association between polyploidy and self-compatibility in facilitates the establishment of neopolyploids by reducing barriers to reproduction in newly formed polyploids, which might otherwise face challenges in finding compatible mates. In terms of adaptations, polyploid plants often display increased cell size, leading to larger organs such as and fruits, which can enhance dispersal and competitiveness. This gigas effect also contributes to improved , as larger cells may improve water storage and hydraulic efficiency in tissues. Representative examples include hexaploid (Triticum aestivum, 6n), which arose from successive polyploidization events and exhibits robust growth in diverse environments, and tetraploid (Coffea arabica, 4n), derived from a single allopolyploidization that supports its commercial viability. Polyploidy drives in through saltational evolution, enabling rapid phenotypic shifts and the formation of new lineages in a single generation. Allopolyploids, in particular, contribute to reticulate phylogenies, where hybrid origins create network-like evolutionary histories rather than strictly bifurcating trees. Emerging since 2020 has revealed that polyploidy alters microbiomes, influencing microbial interactions that affect resistance and niche ; for instance, polyploidy enhances defense against pathogens like , potentially mediated by associations. Despite these advantages, polyploidy presents challenges, particularly meiotic irregularities in odd-ploidy levels (e.g., triploids), where unbalanced segregation leads to sterility and reduced . Many polyploid circumvent this through , an mechanism that bypasses to produce clonal seeds, thereby stabilizing polyploid genotypes and promoting their persistence.

In Animals

Polyploidy is relatively rare in animals compared to plants, occurring in less than 1% of vertebrate species, though it is more prevalent in certain invertebrate groups. In vertebrates, notable examples include tetraploid frogs of the genus Xenopus, such as the allotetraploid Xenopus laevis, which arose from hybridization and genome duplication events. Among fish, salmonids like trout exhibit ancestral autotetraploidy, with linkage relationships in their genomes reflecting a common tetraploid progenitor that underwent rediploidization over evolutionary time. This contrasts with the higher incidence in some invertebrates, where polyploidy contributes to evolutionary diversification without the same germline inheritance challenges seen in vertebrates. In animals, polyploidy often manifests as non-heritable endopolyploidy in somatic tissues, supporting developmental processes rather than stable inheritance. For instance, in Drosophila melanogaster, salivary gland cells undergo repeated DNA replication without cell division, reaching polyteny levels up to 1024n, which enables high gene expression for tissue function. This form of polyploidy is transient and confined to specific cell types, as germline polyploidy is typically inviable or unstable in most animal lineages due to meiotic complications. Specific examples highlight these patterns: the Amazon molly (Poecilia formosa), a gynogenetic fish, produces polyploid offspring through sperm-triggered development without paternal genetic contribution, including rare tetraploid individuals that maintain clonal reproduction. In humans, polyploid conceptions, particularly triploid ones, are rare but significant, comprising approximately 1-2% of recognized pregnancies and accounting for a substantial portion of early miscarriages due to genomic imbalances. Evolutionary constraints explain polyploidy's scarcity in animals, particularly in species with differentiated sex chromosomes. In mammals, failures in dosage compensation—where X-linked gene expression must balance between sexes—exacerbate imbalances in polyploids, often leading to lethality or sterility. Degenerate Y chromosomes in many vertebrates further hinder polyploid speciation by disrupting sex determination and meiotic pairing. Recent studies from 2023 to 2025 underscore polyploidy's role in animal pathology, especially cancer evolution, where whole-genome doubling occurs in over 30% of solid tumors, promoting genomic instability, metastasis, and immune evasion unique to neoplastic contexts.

Evolutionary Role

Speciation Mechanisms

Polyploidy facilitates rapid primarily through mechanisms that establish immediate reproductive barriers between newly formed polyploids and their parental lineages. In allopolyploids, which arise from hybridization followed by genome duplication, this isolation often occurs instantaneously due to postzygotic barriers such as hybrid inviability or failure in crosses with diploid parents. For instance, the merger of divergent genomes leads to dosage imbalances that prevent viable offspring, effectively creating a new in a single generation. This process is exemplified in plants like , where synthetic allopolyploids exhibit strong from their diploid progenitors. Reticulate evolution further complicates speciation in polyploids, as these organisms often represent hybrids of multiple ancestral lineages, resulting in phylogenetic networks rather than strictly bifurcating trees. Allopolyploid formation integrates divergent genomes, leading to mosaic inheritance patterns detectable through incongruent gene trees across loci or among markers. This reticulation promotes by allowing from various sources, as seen in hybrid sunflower species () where chromosomal segments from both parental species contribute to novel adaptive traits and species boundaries. Such network phylogenies underscore polyploidy's role in generating complex evolutionary histories beyond linear descent. Speciation models distinguish between autopolyploidy and allopolyploidy based on underlying genomic processes. Autopolyploid speciation typically involves within-species duplication followed by chromosomal rearrangements, such as inversions or translocations, that reduce fertility in hybrids with diploids and stabilize multivalent pairings during . These rearrangements act as barriers, fostering divergence, as observed in intraspecific hybrids of where fertility reductions open pathways to new lineages. In contrast, allopolyploid speciation proceeds via the merger of two diverged from interspecific hybridization, requiring rapid reconciliation of regulatory networks to resolve conflicts and enable stable inheritance. This genome fusion, as in allopolyploids, immediately isolates the hybrid from parents while providing raw material for subgenome dominance and functional innovation. Polyploids often exhibit elevated speciation rates in certain lineages, leading to higher net diversification compared to diploids in those cases, with evidence from fossil records showing bursts of diversification following whole-genome duplications (WGDs). However, polyploids may face higher rates, leading to debated net effects on long-term diversification. For example, a wave of polyploidy at the Cretaceous-Paleogene boundary correlates with rapid radiations in angiosperms, suggesting WGDs facilitated survival and amid mass extinctions. In microbes, particularly fungi, WGDs similarly drive and diversity; recent analyses reveal convergent evolutionary patterns post-WGD across fungal lineages, enhancing adaptability and lineage splitting in yeasts and mushrooms.

Adaptive Advantages

Polyploidy confers heterosis-like effects through increased , which amplifies the expression of beneficial alleles and enhances overall vigor, growth rates, and stress tolerance in organisms. This phenomenon, akin to hybrid vigor, arises from the additive effects of multiple copies, allowing polyploids to outperform their diploid progenitors under adverse conditions. For example, in (Medicago sativa), whole-genome duplication reprograms the under stress, potentially aiding long-term compared to diploid wild relatives. Similarly, elevated in polyploid crops like and boosts physiological resilience to and by maintaining higher levels of protective proteins and antioxidants. The genomic redundancy inherent in polyploidy promotes plasticity, enabling duplicate s to undergo subfunctionalization—where ancestral functions are partitioned between copies—or neofunctionalization, where one copy acquires novel roles. These evolutionary processes allow polyploids to rapidly adapt to environmental challenges by diversifying gene functions without losing essential activities. In allotetraploid (), for instance, homeologous gene pairs have subfunctionalized to fine-tune fiber development and stress responses, contributing to the ' ecological success. Such divergence facilitates the emergence of traits like altered metabolic pathways, enhancing competitiveness in variable habitats. Polyploids often excel at colonizing marginal or extreme environments, where their physiological robustness provides a selective advantage over diploids. Larger cell sizes and higher metabolic rates in polyploids support of nutrient-scarce or toxic soils; in wild yarrow (Achillea borealis), tetraploid cytotypes predominate in serpentine habitats rich in but low in calcium, due to enhanced metal sequestration and ion homeostasis. Polyploids' larger reproductive structures, including heavier grains, can improve local wind dispersal efficiency in open habitats by increasing pollen viability and adhesion, despite reduced long-distance potential. This niche specialization allows polyploids to exploit resources unavailable to diploids, promoting range expansion. Long-term, polyploidy buffers lineages against by fostering diversification and resilience, with polyploid clades often exhibiting higher rates. In the family, ancient polyploidy events have driven the radiation of speciose lineages like the Triticeae tribe, where duplicated genes facilitated to diverse grasslands and contributed to over 70% of grass being polyploid-derived. This evolutionary longevity stems from redundancy stabilizing core functions while permitting innovation. However, trade-offs exist: genetic redundancy can slow by masking mutations and reducing selective pressure, potentially hindering in stable environments where rapid change is unnecessary.

Detection and Study

Cytogenetic Methods

Cytogenetic methods provide direct visualization and analysis of chromosomes to detect polyploidy, focusing on chromosome number, structure, and behavior during cell division. These techniques rely on microscopic examination of stained cells, offering insights into ploidy levels without requiring advanced molecular tools. Karyotyping involves preparing chromosome spreads from mitotic cells, staining them with dyes such as Giemsa, and counting the total number of chromosomes under a microscope to identify polyploid states, such as triploid (3n) or tetraploid (4n) complements. This method reveals gross chromosomal abnormalities and ploidy but requires well-spread metaphase plates for accuracy. Flow cytometry complements karyotyping by quantifying DNA content in cell suspensions; it measures fluorescence intensity from DNA-binding dyes like propidium iodide, producing histograms with peaks corresponding to DNA amounts, such as 2C for diploid G1 phase and 4C for tetraploid G1 or diploid G2 phase, allowing rapid ploidy estimation in large populations. Meiotic analysis examines pairing during in reproductive cells, such as pollen mother cells, to infer polyploidy. In autopolyploids, multivalents (associations of more than two chromosomes, like quadrivalents) form due to multiple homologous interactions, leading to irregular segregation, whereas allopolyploids often show preferential bivalent between homoeologs from the same subgenome, promoting stability. This , via cytological spreads stained for , helps detect polyploidy and assess implications. Fluorescence in situ hybridization (FISH) enhances detection by using fluorescently labeled DNA probes that bind to specific regions or entire , revealing homoeologs in polyploids. Probes targeting repetitive sequences or unique loci illuminate identities, allowing visualization of multiple genome sets and structural rearrangements in spreads. This technique distinguishes origins in allopolyploids, providing beyond standard . Historically, the Feulgen staining method, developed in the 1920s, enabled early DNA quantification for polyploidy detection by hydrolyzing DNA to create aldehyde groups that react with Schiff's reagent, producing magenta-stained nuclei proportional to DNA content. Measured via microspectrophotometry, this stoichiometric reaction quantified ploidy before flow cytometry, though it was labor-intensive and limited to fixed tissues. Despite their utility, cytogenetic methods have limitations in distinguishing autopolyploidy from allopolyploidy, as chromosome counts alone cannot reveal genomic origins; meiotic pairing data is essential but often inconclusive without additional evidence, and small structural differences may go undetected.

Molecular Techniques

Molecular techniques have revolutionized the study of polyploid genomes by enabling detailed of their , subgenome composition, and evolutionary history through high-throughput sequencing and bioinformatics approaches. These methods address the inherent complexities of polyploidy, such as high heterozygosity and repetitive sequences, which complicate traditional genetic analyses. Key tools include whole-genome sequencing for assembly and phasing, synteny mapping for duplication inference, sequencing for expression patterns, and phylogenetic metrics like Ks plots for dating events. Recent advances in long-read technologies and further enhance resolution and functional validation. Whole-genome sequencing (WGS) of polyploids faces significant challenges due to the presence of multiple similar subgenomes, leading to assembly errors like haplotype collapsing or chimeric contigs. In polyploid , for instance, distinguishing homologous chromosomes is difficult, often resulting in fragmented assemblies with inflated repeat content. Haplotype phasing, which reconstructs individual subgenomes from mixed reads, is crucial for resolving this; tools like WhatsHap polyphase use long reads to accurately phase polyploid , even in regions of high similarity. This approach has enabled haplotype-resolved assemblies in crops like , revealing subgenome-specific variations. Synteny mapping identifies collinear blocks of conserved genes across subgenomes or related , providing for whole-genome duplication (WGD) events in polyploids. By aligning genomes and detecting paralogous segments, researchers infer duplication history; for example, in angiosperms, syntenic blocks reveal ancient WGDs through duplicated chromosomal regions. Tools like WGDI facilitate this by automating cross-species alignments and synteny detection, aiding in the reconstruction of polyploid ancestry. This method is particularly effective for tracing subgenome mergers in allopolyploids. Expression analysis using RNA sequencing (RNA-seq) uncovers dosage effects and homeolog expression biases in polyploids, where duplicated genes may show unequal contributions to the transcriptome. Dosage effects arise from increased gene copy number post-duplication, potentially altering metabolic pathways, while homeolog bias favors expression from one parental subgenome, as observed in resynthesized Brassica allopolyploids. RNA-seq pipelines, such as those employing DESeq2 for differential analysis, quantify these patterns by mapping reads to phased subgenomes, revealing biases in up to 20-30% of homeolog pairs in wheat. This highlights regulatory divergence following polyploidization. Phylogenetic tools, particularly Ks plots, estimate the age of duplications by plotting the distribution of synonymous substitutions per site (Ks) between paralogous genes. Ks represents the number of synonymous substitutions per synonymous site, serving as a for neutral ; peaks in Ks distributions indicate synchronous WGD events, with lower Ks values signaling more recent duplications. Ks is calculated via the Poisson correction model, which accounts for multiple substitutions at the same site using the formula Ks=−ln⁡(1−dL)K_s = -\ln(1 - \frac{d}{L}), where dd is the observed number of synonymous differences and LL is the number of synonymous sites, assuming a Poisson process of substitutions. In polyploid studies, Ks plots have dated events like the rho WGD in grasses to approximately 60-70 million years ago. Advances in long-read sequencing, such as PacBio's HiFi reads in the 2020s, have significantly improved polyploid genome resolution by producing accurate, long contigs that span repetitive regions and resolve subgenomes without collapsing haplotypes. For example, HiFi sequencing achieved a BUSCO completeness score of 96.8% in the tetraploid Altus assembly, enabling precise structural variant detection. Complementing this, CRISPR-based validates polyploid structures by targeting specific homeologs, confirming functional roles; in polyploid , CRISPR/ has edited subgenome-specific loci to study dosage compensation, with efficiencies up to 50% in edited lines. These tools collectively enhance the precision of polyploid research.

Applications and Implications

Agricultural Uses

Polyploidy plays a central role in agricultural breeding strategies, where it is often induced artificially to enhance crop yields and desirable traits. Breeders commonly use chemical agents like to double sets, creating polyploids that exhibit larger cell sizes and increased vigor, leading to higher production. A prominent example is the development of seedless watermelons through triploid hybrids, formed by crossing tetraploid females (induced via ) with diploid males, resulting in sterile fruits with improved fruit quality and market value. This approach not only boosts yield per but also addresses consumer preferences for seedless varieties, demonstrating polyploidy's utility in targeted trait improvement. Many major crops are polyploid, with approximately 75% of domesticated species exhibiting polyploidy, often stemming from ancient whole-genome duplications (WGDs). For instance, bread (Triticum aestivum) is a hexaploid resulting from multiple WGD events, contributing to its adaptability and high yield, while (), though diploid, shows evidence of ancient WGDs that facilitated its domestication and resilience. Synthetic polyploids like , a hexaploid hybrid of and created by chromosome doubling of the sterile wheat-rye hybrid, combine wheat's yield potential with rye's disease resistance and environmental tolerance, making it a valuable for marginal lands. These natural and engineered polyploids form the backbone of staple crop production worldwide. The benefits of polyploidy in agriculture include enhanced biomass accumulation due to larger cells and organs, as well as improved resistance to diseases and environmental stresses. In potatoes (Solanum tuberosum), which are predominantly autotetraploid, polyploidy correlates with increased tuber size and yield, supporting higher starch content and overall productivity essential for food staples. Polyploids often show greater heterozygosity and gene redundancy, conferring advantages like pathogen resistance in crops such as and . However, breeding challenges persist, particularly the "triploid block," where triploid progeny from interploidy crosses suffer reduced fertility and viability due to endosperm imbalances, complicating hybridization efforts. Recent advances in have addressed some limitations, with genetically modified (GMO) polyploids emerging to tackle climate challenges; for example, CRISPR-edited polyploid lines have shown promise in enhancing through targeted gene modifications that improve water-use efficiency. Overall, polyploids underpin global by enabling higher yields and resilience in key crops, contributing to amid growing demands. Their economic impact is profound, as polyploid varieties in commodities like , potatoes, and bananas support billions in annual production and help mitigate food shortages.

Medical Relevance

Polyploidy manifests in human medicine primarily through rare chromosomal anomalies and acquired cellular states that contribute to pathology. Triploidy, characterized by an extra set of chromosomes resulting in 69 total chromosomes, represents a severe form of polyploidy and occurs in approximately 1-3% of conceptions, though most cases result in spontaneous due to profound developmental disruptions. Survivors, often with partial triploidy mosaicism, exhibit syndromes involving growth abnormalities, organ malformations, and , with lethality typically occurring in utero or shortly after birth. These conditions arise from errors in fertilization, such as dispermy or failure of , leading to unbalanced that disrupts embryonic development. In , whole-genome doubling (WGD), a polyploid event, plays a pivotal role in tumorigenesis by generating tetraploid cells that exhibit genomic instability and promote , facilitating tumor evolution and progression. WGD is detected in approximately 37% of primary solid tumors and up to 56% of metastatic ones, often occurring early in cancer development and correlating with poor in various malignancies. This process enhances cellular adaptability, enabling resistance to therapies and metastatic potential through and other structural variations. Therapeutically, polyploid cell models, particularly polyploid giant cancer cells (PGCCs), have emerged as valuable tools for drug screening, as they recapitulate therapy resistance mechanisms observed in patient tumors. High-throughput platforms using these models identify compounds that selectively target polyploid subpopulations, addressing the heterogeneity that contributes to treatment failure in cancers like and . Additionally, gene editing approaches, such as /, offer potential for targeting duplicate gene copies in polyploid cancer cells to exploit their genomic vulnerabilities and restore balanced expression. These strategies aim to induce by disrupting redundant pathways unique to polyploid states. From an perspective, ancient whole-genome duplications (WGDs) in s, as posited by the 2R hypothesis, involved two rounds approximately 500 million years ago, providing raw material for the evolution of complex traits including the . These events duplicated key gene families, such as those encoding (MHC) molecules and Hox clusters, enabling subfunctionalization that underpinned vertebrate innovations like enhanced immunity and organ complexity. Recent research highlights emerging links between polyploidy and neurodegeneration, particularly neuronal endopolyploidy in (AD), where cell cycle re-entry in post-mitotic neurons leads to without division, resulting in hyperploid states that may exacerbate tau pathology and synaptic loss. A 2024 study indicates that such events in aging neurons lead to and accumulate genomic instability, contributing to AD progression, though therapeutic interventions remain exploratory.

References

  1. https://www.nature.com/scitable/topicpage/polyploidy-1552814/
  2. https://pmc.ncbi.nlm.nih.gov/articles/PMC7484144/
  3. https://pmc.ncbi.nlm.nih.gov/articles/PMC6772149/
  4. https://www.sciencedirect.com/science/article/pii/S0065266008604903
  5. https://pmc.ncbi.nlm.nih.gov/articles/PMC8136868/
  6. https://www.nature.com/articles/hdy201279
  7. https://pbea.agron.iastate.edu/files/2021/11/Ploidy-Polyploidy-Aneuploidy-Haploidy.pdf
  8. https://www.pnas.org/doi/10.1073/pnas.0811575106
  9. https://bsapubs.onlinelibrary.wiley.com/doi/10.3732/ajb.1400178
  10. https://www.journals.uchicago.edu/doi/10.1086/700636
  11. https://www.sciencedirect.com/science/article/pii/S2590346220301176
  12. https://bio.libretexts.org/Bookshelves/Agriculture_and_Horticulture/Crop_Genetics_%28Suza_and_Lamkey%29/01%253A_Chapters/1.10%253A_Ploidy-_Polyploidy_Aneuploidy_and_Haploidy
  13. https://bio.libretexts.org/Courses/City_College_of_San_Francisco/Introduction_to_Genetics/02%253A_Cells_and_Mitosis/2.06%253A_Chromosomes_Mitosis_and_Meiosis/2.6.02%253A_Polyploidy_Arises_from_Changes_in_Whole_Sets_of_Chromosomes
  14. https://iastate.pressbooks.pub/cropgenetics/chapter/ploidy-polyploidy-aneuploidy-haploidy-2/
  15. https://pmc.ncbi.nlm.nih.gov/articles/PMC8535482/
  16. https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/ploidy
  17. https://www.annualreviews.org/doi/pdf/10.1146/annurev.genet.34.1.401
  18. https://rotel.pressbooks.pub/genetics/chapter/differences-in-ploidy-and-the-impact-to-meiosis-3/
  19. https://pmc.ncbi.nlm.nih.gov/articles/PMC7618257/
  20. https://oertx.highered.texas.gov/courseware/lesson/1703/overview
  21. https://opened.cuny.edu/courseware/lesson/697/student/?section=5
  22. https://pmc.ncbi.nlm.nih.gov/articles/PMC6681243/
  23. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/autopolyploidy
  24. https://bsapubs.onlinelibrary.wiley.com/doi/10.1002/ajb2.70047
  25. https://pmc.ncbi.nlm.nih.gov/articles/PMC3554449/
  26. https://pmc.ncbi.nlm.nih.gov/articles/PMC3430260/
  27. https://pmc.ncbi.nlm.nih.gov/articles/PMC2710212/
  28. https://pmc.ncbi.nlm.nih.gov/articles/PMC2980832/
  29. https://pmc.ncbi.nlm.nih.gov/articles/PMC3522158/
  30. https://pmc.ncbi.nlm.nih.gov/articles/PMC11431062/
  31. https://pmc.ncbi.nlm.nih.gov/articles/PMC9904339/
  32. https://pmc.ncbi.nlm.nih.gov/articles/PMC1462064/
  33. https://pmc.ncbi.nlm.nih.gov/articles/PMC5567635/
  34. https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.20437
  35. https://nph.onlinelibrary.wiley.com/doi/full/10.1046/j.1469-8137.2003.00926.x
  36. https://pmc.ncbi.nlm.nih.gov/articles/PMC1526671/
  37. https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2021.589160/full
  38. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0003353
  39. https://academic.oup.com/biolinnean/article/82/4/475/2643080
  40. https://www.pnas.org/doi/10.1073/pnas.1112041109
  41. https://academic.oup.com/evolut/article-abstract/64/7/1984/6854310
  42. https://pmc.ncbi.nlm.nih.gov/articles/PMC11134461/
  43. https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/paleopolyploidy
  44. https://www.karger.com/Article/Pdf/125999
  45. https://genome.cshlp.org/content/16/7/934.full.pdf
  46. https://www.nature.com/articles/42711
  47. https://pubmed.ncbi.nlm.nih.gov/15208399/
  48. https://bsapubs.onlinelibrary.wiley.com/doi/10.1002/ajb2.1056
  49. https://pubmed.ncbi.nlm.nih.gov/17707623/
  50. https://www.cell.com/molecular-plant/fulltext/S1674-2052(19)30359-4
  51. https://pmc.ncbi.nlm.nih.gov/articles/PMC2821985/
  52. https://pmc.ncbi.nlm.nih.gov/articles/PMC7332690/
  53. https://pmc.ncbi.nlm.nih.gov/articles/PMC2988484/
  54. https://link.springer.com/article/10.1007/s10681-009-9998-0
  55. https://www.sciencedirect.com/science/article/abs/pii/S0304377021001339
  56. https://pmc.ncbi.nlm.nih.gov/articles/PMC4571729/
  57. https://bmcecolevol.biomedcentral.com/articles/10.1186/1471-2148-14-20
  58. https://pubmed.ncbi.nlm.nih.gov/38748576/
  59. https://onlinelibrary.wiley.com/doi/10.1111/jse.12909
  60. https://www.sciencedirect.com/science/article/pii/S1674205214000379
  61. https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.16396
  62. https://academic.oup.com/aob/article/109/1/19/154024
  63. https://pmc.ncbi.nlm.nih.gov/articles/PMC9441891/
  64. https://pmc.ncbi.nlm.nih.gov/articles/PMC6925018/
  65. https://www.nature.com/articles/s41598-020-61216-7
  66. https://academic.oup.com/plcell/article/33/1/11/6015242
  67. https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.17105
  68. https://www.sciencedirect.com/science/article/pii/S0960982222007746
  69. https://pmc.ncbi.nlm.nih.gov/articles/PMC5521839/
  70. https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.12954
  71. https://pmc.ncbi.nlm.nih.gov/articles/PMC10044425/
  72. https://www.nature.com/articles/nature19840
  73. https://pubmed.ncbi.nlm.nih.gov/3623080/
  74. https://www.sdbonline.org/sites/fly/aimorph/puffing.htm
  75. https://academic.oup.com/jhered/article/99/2/223/2187701
  76. https://www.sciencedirect.com/topics/neuroscience/triploidy
  77. https://karger.com/cgr/article/140/2-4/256/62187/Polyploidy-in-Animals-Effects-of-Gene-Expression
  78. https://www.jstor.org/stable/2462166
  79. https://www.nature.com/articles/s41586-023-05794-2
  80. https://www.nature.com/articles/s41586-025-09240-3
  81. https://www.pnas.org/doi/10.1073/pnas.2217672120
  82. https://www.pnas.org/doi/10.1073/pnas.0805141105
  83. https://pmc.ncbi.nlm.nih.gov/articles/PMC2493047/
  84. https://pmc.ncbi.nlm.nih.gov/articles/PMC11342234/
  85. https://nph.onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.2009.03142.x
  86. https://pmc.ncbi.nlm.nih.gov/articles/PMC2684529/
  87. https://www.science.org/doi/10.1126/science.1207205
  88. https://bsapubs.onlinelibrary.wiley.com/doi/10.1002/ajb2.1060
  89. https://pmc.ncbi.nlm.nih.gov/articles/PMC4071526/
  90. https://academic.oup.com/g3journal/article/12/6/jkac094/6572348
  91. https://pmc.ncbi.nlm.nih.gov/articles/PMC12417302/
  92. https://www.nature.com/articles/s41467-020-17302-5
  93. https://www.pnas.org/doi/10.1073/pnas.1016631108
  94. https://academic.oup.com/aob/article/113/7/1175/2769091
  95. https://www.pnas.org/doi/10.1073/pnas.0630618100
  96. https://genomebiology.biomedcentral.com/articles/10.1186/s13059-019-1650-2
  97. https://pmc.ncbi.nlm.nih.gov/articles/PMC9609754/
  98. https://pmc.ncbi.nlm.nih.gov/articles/PMC8306847/
  99. https://nph.onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.2009.03084.x
  100. https://pubmed.ncbi.nlm.nih.gov/17577417/
  101. https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.00526/full
  102. https://pmc.ncbi.nlm.nih.gov/articles/PMC11227455/
  103. https://www.sciencedirect.com/topics/immunology-and-microbiology/feulgen-staining
  104. https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.13698
  105. https://genomebiology.biomedcentral.com/articles/10.1186/s13059-020-02158-1
  106. https://genomebiology.biomedcentral.com/articles/10.1186/s13059-023-03160-z
  107. https://www.sciencedirect.com/science/article/pii/S1674205222003707
  108. https://pmc.ncbi.nlm.nih.gov/articles/PMC4145114/
  109. https://pmc.ncbi.nlm.nih.gov/articles/PMC6218233/
  110. https://www.nature.com/articles/hdy201294
  111. https://pmc.ncbi.nlm.nih.gov/articles/PMC6225891/
  112. https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2023.1152468/full
  113. https://www.researchgate.net/figure/Polyploidy-in-Plant-Breeding-Strategies_tbl1_385802561
  114. https://www.nature.com/articles/s41598-023-32225-z
  115. https://pmc.ncbi.nlm.nih.gov/articles/PMC12403409/
  116. https://acsess.onlinelibrary.wiley.com/doi/abs/10.2135/cropsci1969.0011183X000900020026x
  117. https://www.sciencedirect.com/science/article/pii/S0168952525000708
  118. https://academic.oup.com/jxb/article/76/8/2096/8029463
  119. https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2025.1598947/full
  120. https://phys.org/news/2024-04-polyploidy-vegetables-exploring-genetics-crop.html
  121. https://www.webmd.com/baby/triploidy-what-to-know
  122. https://rarediseases.org/rare-diseases/triploidy/
  123. https://www.urmc.rochester.edu/pathology-labs/work-learning-resources/pediatric-pathology/triploidy.aspx
  124. https://pmc.ncbi.nlm.nih.gov/articles/PMC10840902/
  125. https://pmc.ncbi.nlm.nih.gov/articles/PMC7889737/
  126. https://pubs.acs.org/doi/10.1021/acs.analchem.4c05138
  127. https://www.nature.com/articles/s41420-024-02206-w
  128. https://www.nature.com/articles/s41559-023-02299-z
  129. https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3002559
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