Condition where cells have more than two sets of chromosomes
Not to be confused with "polypoid", resembling apolyp.
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 thecells of anorganism have more than two paired sets of (homologous)chromosomes. Most species whose cells havenuclei (eukaryotes) arediploid, 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 arepolyploid. Polyploidy is especially common in plants. Most eukaryotes have diploidsomatic cells, but producehaploidgametes (eggs and sperm) bymeiosis. Amonoploid has only one set of chromosomes, and the term is usually only applied to cells or organisms that are normally diploid. Males ofbees and otherHymenoptera, for example, are monoploid. Unlike animals,plants and multicellularalgae havelife cycles with twoalternating multicellular generations. Thegametophyte generation is haploid, and produces gametes bymitosis; thesporophyte generation is diploid and producesspores bymeiosis.
Polyploidy is the result of whole-genome duplication during the evolution of species. It may occur due to abnormalcell 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 andcell cultures by some chemicals: the best known iscolchicine, 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.
Amongmammals, 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 otheranimals, such asgoldfish,[3]salmon, andsalamanders. It is common amongferns and floweringplants (seeHibiscus rosa-sinensis), including both wild and cultivatedspecies.Wheat, for example, after millennia ofhybridization and modification by humans, has strains that arediploid (two sets of chromosomes),tetraploid (four sets of chromosomes) with the common name ofdurum or macaroni wheat, andhexaploid (six sets of chromosomes) with the common name of bread wheat. Many agriculturally important plants of the genusBrassica are also tetraploids.Sugarcane can have ploidy levels higher thanoctaploid.[4]
Polyploidization can be a mechanism of sympatric speciation because polyploids are usually unable to interbreed with their diploid ancestors. An example is the plantErythranthe peregrina. Sequencing confirmed that this species originated fromE. × robertsii, a sterile triploid hybrid betweenE. guttata andE. lutea, both of which have been introduced and naturalised in the United Kingdom. New populations ofE. peregrina arose onthe Scottish mainland and theOrkney Islands via genome duplication from local populations ofE. × 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 inArabidopsis arenosa andArabidopsis 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.[10]
"Triploid" redirects here. For the human chromosomal disorder (69 XXX, etc.), seeTriploid syndrome.
Organ-specific patterns of endopolyploidy (from 2x to 64x) in the giant antDinoponera australis
Polyploid types are labeled according to the number of chromosome sets in thenucleus. The letterx is used to represent the number of chromosomes in a single set:
Autopolyploids are polyploids with multiple chromosome sets derived from a singletaxon.
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 oftriploid 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 thetriploid bridge.[21] Triploids may also persist throughasexual reproduction. In fact, stable autotriploidy in plants is often associated withapomictic mating systems.[22] In agricultural systems, autotriploidy can result in seedlessness, as inwatermelons andbananas.[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 asprotoplast fusion or treatment withcolchicine,oryzalin ormitotic inhibitors are used to disrupt normalmitotic 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 threehomologous chromosome sets, which can lead to high rates of multivalent pairing duringmeiosis (particularly in recently formed autopolyploids, also known as neopolyploids) and an associated decrease in fertility due to the production ofaneuploid 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 inArabidopsis arenosa[29] andArabidopsis lyrata,[30] with specific adaptive alleles of these species shared between only the evolved polyploids.[31][32]
The high degree ofhomology among duplicated chromosomes causes autopolyploids to displaypolysomic inheritance.[33] 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.[34] 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.[35][36]
About half of all polyploids are thought to be the result of autopolyploidy,[37][38] although many factors make this proportion hard to estimate.[39]
Allopolyploids oramphipolyploids orheteropolyploids 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 afterhybridization. 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 diploidF1 hybrids produce unreduced gametes that fuse to form allopolyploid progeny.[40] 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 betweenhomoeologous chromosomes ornondisjunction during meiosis.[40] 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][34]
Because pairing between homoeologous chromosomes is rare in established allopolyploids, they may benefit from fixedheterozygosity of homoeologous alleles.[41] In certain cases, such heterozygosity can have beneficialheterotic 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 breadwheat andtriticale are examples of an allopolyploids with six chromosome sets.Cotton,peanut, andquinoa are allotetraploids with multiple origins. InBrassicaceous crops, theTriangle of U describes the relationships between the three common diploid Brassicas (B. oleracea,B. rapa, andB. nigra) and three allotetraploids (B. napus,B. juncea, andB. carinata) derived from hybridization among the diploid species. A similar relationship exists between three diploid species ofTragopogon (T. dubius,T. pratensis, andT. porrifolius) and two allotetraploid species (T. mirus andT. miscellus).[42] Complex patterns of allopolyploid evolution have also been observed in animals, as in the frog genusXenopus.[43]
Organisms in which a particular chromosome, or chromosome segment, is under- or over-represented are said to beaneuploid (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.[44]
Polyploidy occurs in some tissues of animals that are otherwise diploid, such as humanmuscle tissues.[45] This is known asendopolyploidy. Species whose cells do not have nuclei, that is,prokaryotes, may be polyploid, as seen in the largebacteriumEpulopiscium fishelsoni.[46] Henceploidy is defined with respect to a cell.
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 ishaploid.
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.
Ancient genome duplications probably occurred in the evolutionary history of all life. Duplication events that occurred long ago in the history of variousevolutionary lineages can be difficult to detect because of subsequentdiploidization (such that a polyploid starts to behave cytogenetically as a diploid over time) asmutations 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.[47]
A karyotype is the characteristic chromosome complement of aeukaryotespecies.[49][50] The preparation and study of karyotypes is part ofcytology and, more specifically,cytogenetics.
Although the replication and transcription of DNA is highly standardized ineukaryotes, 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 are those brought together followinginter-species hybridization andallopolyploidization, 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 speciesTriticum urartu andAegilops 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 ahybrid genome with two sets of chromosomes derived fromTriticum urartu and two sets of chromosomes derived fromAegilops speltoides. Each chromosome pair derived from theTriticum urartu parent ishomoeologous to the opposite chromosome pair derived from theAegilops speltoides parent, though each chromosome pair unto itself ishomologous.
Examples in animals are more common in non-vertebrates[51] such asflatworms,leeches, andbrine shrimp. Within vertebrates, examples of stable polyploidy include thesalmonids and manycyprinids (i.e.carp).[52] Some fish have as many as 400 chromosomes.[52] Polyploidy also occurs commonly in amphibians; for example the biomedically important genusXenopus contains many different species with as many as 12 sets of chromosomes (dodecaploid).[53] Polyploid lizards are also quite common. Most are sterile and reproduce byparthenogenesis;[citation needed] others, likeLiolaemus chiliensis, maintain sexual reproduction. Polyploidmole salamanders (mostly triploids) are all female and reproduce bykleptogenesis,[54] "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 asparenchymal liver cells, are polyploid,[55][56] rare instances of polyploidmammals are known, but most often result inprenatal death. Anoctodontidrodent ofArgentina's harshdesert regions, known as theplains viscacha rat (Tympanoctomys barrerae) has been reported as an exception to this 'rule'.[57] However, careful analysis using chromosome paints shows that there are only two copies of each chromosome inT. barrerae, not the four expected if it were truly a tetraploid.[58] This rodent is not arat, but kin toguinea pigs andchinchillas. Its "new" diploid (2n) number is 102 and so its cells are roughly twice normal size. Its closest living relation isOctomys mimax, theAndean Viscacha-Rat of the same family, whose 2n = 56. It was therefore surmised that anOctomys-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 byHar Swarup (1956) using a cold-shock treatment of the eggs close to the time of fertilization, which produced triploid embryos that successfully matured.[59][60] Cold or heat shock has also been shown to result in unreduced amphibian gametes, though this occurs more commonly in eggs than in sperm.[61]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.[62] The British scientistJ. 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 byShinya 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.[62]
True polyploidy rarely occurs in humans, although polyploid cells occur in highlydifferentiated tissue, such as liverparenchyma, heart muscle, placenta and in bone marrow.[63][64]Aneuploidy is more common.
Polyploidy occurs in humans in the form oftriploidy, with 69 chromosomes (sometimes called 69, XXX), and tetraploidy with 92 chromosomes (sometimes called 92, XXXX). Triploidy, usually due topolyspermy, occurs in about 2–3% of all human pregnancies and ~15% of miscarriages.[citation needed] The vast majority of triploid conceptions end as amiscarriage; those that do survive to term typically die shortly after birth. In some cases, survival past birth may be extended if there ismixoploidy with both adiploid 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 aPneumocystis carinii infection, which indicates a weak immune system.[65]
Triploidy may be the result of eitherdigyny (the extra haploid set is from the mother) ordiandry (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.[66] Digyny is most commonly caused by either failure of one meiotic division during oogenesis leading to a diploidoocyte or failure to extrude onepolar body from theoocyte. Diandry appears to predominate among earlymiscarriages, while digyny predominates among triploid zygotes that survive into the fetal period.[67] However, among early miscarriages, digyny is also more common in those cases less than8+1⁄2 weeks gestational age or those in which an embryo is present. There are also two distinctphenotypes in triploidplacentas andfetuses that are dependent on the origin of the extrahaploid set. In digyny, there is typically an asymmetric poorly grownfetus, with markedadrenalhypoplasia and a very smallplacenta.[68] In diandry, a partialhydatidiform mole develops.[66] These parent-of-origin effects reflect the effects ofgenomic 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 atprenatal diagnosis and these are generally considered 'harmless'. It is not clear whether these tetraploid cells simply tend to arise duringin vitro cell culture or whether they are also present in placental cellsin 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.
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.[69][70][71][72] Huge explosions inangiosperm species diversity appear to have coincided with the timing of ancient genome duplications shared by many species.[73] It has been established that 15% of angiosperm and 31% of fernspeciation events are accompanied by ploidy increase.[74]
Polyploid plants can arise spontaneously in nature by several mechanisms, including meiotic or mitotic failures, and fusion of unreduced (2n) gametes.[41] Both autopolyploids (e.g. potato[75]) 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 ofspeciation and eco-niche exploitation.[70][41] 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, andepigenetic remodeling, all of which affect gene content and/or expression levels.[76][77][78][79] Many of these rapid changes may contribute to reproductive isolation and speciation. However, seed generated frominterploidy crosses, such as between polyploids and their parent species, usually have aberrant endosperm development which impairs their viability,[80][81] thus contributing topolyploid speciation. Polyploids may also interbreed with diploids and produce polyploid seeds, as observed in the agamic complexes ofCrepis.[82]
Some plants are triploid. Asmeiosis is disturbed, these plants are sterile, with all plants having the same genetic constitution: Among them, the exclusively vegetatively propagatedsaffron crocus (Crocus sativus). Also, the extremely rare Tasmanian shrubLomatia tasmanica is a triploid sterile species.
There are few naturally occurring polyploidconifers.[83] One example is the Coast RedwoodSequoia sempervirens, which is a hexaploid (6x) with 66 chromosomes (2n = 6x = 66), although the origin is unclear.[84]
Aquatic plants, especially theMonocotyledons, include a large number of polyploids.[85]
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 ofwheat (Triticum turgidum) andrye (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 asgrafting.
Polyploidy in crop plants is most commonly induced by treating seeds with the chemicalcolchicine.
Some crops are found in a variety of ploidies:tulips andlilies are commonly found as both diploid and triploid;daylilies (Hemerocallis cultivars) are available as either diploid or tetraploid; apples andkinnow mandarins can be diploid, triploid, or tetraploid.
Besides plants and animals, the evolutionary history of variousfungal species is dotted by past and recent whole-genome duplication events (see Albertin and Marullo 2012[89] for review). Several examples of polyploids are known:
In addition, polyploidy is frequently associated withhybridization and reticulate evolution that appear to be highly prevalent in several fungal taxa. Indeed,homoploid speciation (hybrid speciation without a change inchromosome number) has been evidenced for some fungal species (such as thebasidiomycotaMicrobotryum violaceum[97]).
Schematic phylogeny of the Chromalveolata. Red circles indicate polyploidy, blue squares indicate hybridization. From Albertin and Marullo, 2012[89]
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 polyploidSaccharomyces genomes strikingly reflect the evolutionary fate of plant polyploid ones. Large chromosomal rearrangements[98] leading tochimeric chromosomes[99] have been described, as well as more punctual genetic modifications such as gene loss.[100] The homoealleles of the allotetraploid yeastS. pastorianus show unequal contribution to thetranscriptome.[101]Phenotypic diversification is also observed following polyploidization and/or hybridization in fungi,[102] producing the fuel fornatural selection and subsequentadaptation and speciation.
Other eukaryotictaxa have experienced one or more polyploidization events during their evolutionary history (see Albertin and Marullo, 2012[89] for review). Theoomycetes, which are non-true fungi members, contain several examples of paleopolyploid and polyploid species, such as within the genusPhytophthora.[103] Some species of brownalgae (Fucales, Laminariales[104] anddiatoms[105]) contain apparent polyploid genomes. In theAlveolata group, the remarkable speciesParamecium tetraurelia underwent three successive rounds of whole-genome duplication[106] and established itself as a major model for paleopolyploid studies.
Azotobacter vinelandii can contain up to 80 chromosome copies per cell.[109] However this is only observed in fast growing cultures, whereas cultures grown in synthetic minimal media are not polyploid.[110]
^Ohno S, Muramoto J, Christian L, Atkin NB (1967). "Diploid-tetraploid relationship among old-world members of the fish family Cyprinidae".Chromosoma.23 (1):1–9.doi:10.1007/BF00293307.
Manimekalai R, Suresh G, Govinda Kurup H, Athiappan S, Kandalam M (September 2020). "Role of NGS and SNP genotyping methods in sugarcane improvement programs".Critical Reviews in Biotechnology.40 (6):865–880.doi:10.1080/07388551.2020.1765730.PMID32508157.
^abCrowhurst, Ross N.; Whittaker, D.; Gardner, R. C. (April 1992). "THE GENETIC ORIGIN OF KIWIFRUIT".Acta Horticulturae (297):61–62.doi:10.17660/ActaHortic.1992.297.5.
^Varoquaux F, Blanvillain R, Delseny M, Gallois P (June 2000). "Less is better: new approaches for seedless fruit production".Trends in Biotechnology.18 (6):233–242.doi:10.1016/s0167-7799(00)01448-7.PMID10802558.
^Cotter D, O'Donovan V, O'Maoiléidigh N, Rogan G, Roche N, Wilkins NP (June 2000). "An evaluation of the use of triploid Atlantic salmon (Salmo salar L.) in minimising the impact of escaped farmed salmon on wild populations".Aquaculture.186 (1–2):61–75.Bibcode:2000Aquac.186...61C.doi:10.1016/S0044-8486(99)00367-1.
^Dermen H (May 1951). "Tetraploid and Diploid Adventitious Shoots: From a Giant Sport of McIntosh Apple".Journal of Heredity.42 (3):145–149.doi:10.1093/oxfordjournals.jhered.a106189.
^abLe Comber SC, Ainouche ML, Kovarik A, Leitch AR (April 2010). "Making a functional diploid: from polysomic to disomic inheritance".The New Phytologist.186 (1):113–122.doi:10.1111/j.1469-8137.2009.03117.x.PMID20028473.
^Stebbins GL (1950).Variation and Evolution in Plants. Oxford University Press.[page needed]
^Ramsey J, Schemske DW (January 1998). "Pathways, Mechanisms, and Rates of Polyploid Formation in Flowering Plants".Annual Review of Ecology and Systematics.29 (1):467–501.doi:10.1146/annurev.ecolsys.29.1.467.
^abRamsey J (January 1998). "Pathways, Mechanisms, and Rates of Polyploid Formation in Flowering Plants".Annual Review of Ecology and Systematics.29 (1):467–501.doi:10.1146/annurev.ecolsys.29.1.467.
^abcComai L (November 2005). "The advantages and disadvantages of being polyploid".Nature Reviews. Genetics.6 (11):836–846.doi:10.1038/nrg1711.PMID16304599.
^Ownbey M (January 1950). "Natural Hybridization and Amphiploidy in the Genus Tragopogon".American Journal of Botany.37 (7):487–499.doi:10.2307/2438023.JSTOR2438023.
^Cannatella DC, De Sa RO (1993). "Xenopus laevis as a Model Organism".Society of Systematic Biologists.42 (4):476–507.doi:10.1093/sysbio/42.4.476.
^Bogart JP, Bi K, Fu J, Noble DW, Niedzwiecki J (February 2007). "Unisexual salamanders (genus Ambystoma) present a new reproductive mode for eukaryotes".Genome.50 (2):119–136.doi:10.1139/g06-152.PMID17546077.
^Winkelmann M, Pfitzer P, Schneider W (December 1987). "Significance of polyploidy in megakaryocytes and other cells in health and tumor disease".Klinische Wochenschrift.65 (23):1115–1131.doi:10.1007/BF01734832.PMID3323647.
^"Triploidy". National Organization for Rare Disorders. Retrieved2018-12-23.
^De Bodt S, Maere S, Van de Peer Y (November 2005). "Genome duplication and the origin of angiosperms".Trends in Ecology & Evolution.20 (11):591–597.doi:10.1016/j.tree.2005.07.008.PMID16701441.
^von Wangenheim KH, Peterson HP (June 2004). "Aberrant endosperm development in interploidy crosses reveals a timer of differentiation".Developmental Biology.270 (2):277–289.doi:10.1016/j.ydbio.2004.03.014.PMID15183714.
^Ahuja MR, Neale DB (2002). "Origins of Polyploidy in Coast Redwood (Sequoia sempervirens (D. Don) Endl.) and Relationship of Coast Redwood to other Genera of Taxodiaceae".Silvae Genetica.51:2–3.INIST13965465.
^Les DH, Philbrick CT (1993). "Studies of hybridization and chromosome number variation in aquatic angiosperms: Evolutionary implications".Aquatic Botany.44 (2–3):181–228.Bibcode:1993AqBot..44..181L.doi:10.1016/0304-3770(93)90071-4.
^Emshwiller E (2006). "Origins of polyploid crops: The example of the octaploid tuber cropOxalis tuberosa". In Zeder MA, Decker-Walters D, Emshwiller E, Bradley D, Smith BD (eds.).Documenting Domestication: New Genetic and Archaeological Paradigms. Berkeley, CA: University of California Press. pp. 153–168.ISBN978-0-520-24638-6.
^Devier B, Aguileta G, Hood ME, Giraud T (2009). "Using phylogenies of pheromone receptor genes in the Microbotryum violaceum species complex to investigate possible speciation by hybridization".Mycologia.102 (3):689–696.doi:10.3852/09-192.PMID20524600.
^Minato T, Yoshida S, Ishiguro T, Shimada E, Mizutani S, Kobayashi O, Yoshimoto H (March 2009). "Expression profiling of the bottom fermenting yeast Saccharomyces pastorianus orthologous genes using oligonucleotide microarrays".Yeast.26 (3):147–165.doi:10.1002/yea.1654.PMID19243081.
^Zahradka K, Slade D, Bailone A, Sommer S, Averbeck D, Petranovic M, et al. (October 2006). "Reassembly of shattered chromosomes in Deinococcus radiodurans".Nature.443 (7111):569–573.Bibcode:2006Natur.443..569Z.doi:10.1038/nature05160.PMID17006450.
^Soppa J (January 2011). "Ploidy and gene conversion in Archaea".Biochemical Society Transactions.39 (1):150–154.doi:10.1042/BST0390150.PMID21265763.
^Kottemann M, Kish A, Iloanusi C, Bjork S, DiRuggiero J (June 2005). "Physiological responses of the halophilic archaeon Halobacterium sp. strain NRC1 to desiccation and gamma irradiation".Extremophiles.9 (3):219–227.doi:10.1007/s00792-005-0437-4.PMID15844015.
Raes J, Vandepoele K, Simillion C, Saeys Y, Van de Peer Y (2003). "Investigating ancient duplication events in the Arabidopsis genome".Journal of Structural and Functional Genomics.3 (1–4):117–129.doi:10.1023/A:1022666020026.PMID12836691.
Soltis DE,Soltis PS, Schemske DW, Hancock JF, Thompson JN, Husband BC, Judd WS (2007). "Autopolyploidy in Angiosperms: Have We Grossly Underestimated the Number of Species?".Taxon.56 (1):13–30.JSTOR25065732.
Soltis DE, Buggs RJ, Doyle JJ, Soltis PS (2010). "What we still don't know about polyploidy".Taxon.59 (5):1387–1403.doi:10.1002/tax.595006.
Van de Peer Y, Taylor JS, Meyer A (2003). "Are all fishes ancient polyploids?".Journal of Structural and Functional Genomics.3 (1–4):65–73.doi:10.1023/A:1022652814749.PMID12836686.
Wolfe KH (May 2001). "Yesterday's polyploids and the mystery of diploidization".Nature Reviews. Genetics.2 (5):333–341.doi:10.1038/35072009.PMID11331899.
