Polyploid

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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.

Polyploid cells and organisms are those containing more than two paired (homologous) sets of chromosomes. Most eukaryotic species are diploid, meaning they have two sets of chromosomes — one set inherited from each parent. However polyploidy is found in some organisms and is especially common in plants. In addition, polyploidy also occurs in some tissues of animals who are otherwise diploid, such as human muscle tissues.[1] This is known as endopolyploidy. (Monoploid organisms also occur; a monoploid has only one set of chromosomes. These include the vast majority of prokaryotes.)

Polyploidy refers to a numerical change in a whole set of chromosomes. Organisms in which a particular chromosome, or chromosome segment, is under- or overrepresented are said to be aneuploid (from the Greek words meaning "not," "good," and "fold"). Therefore the distinction between aneuploidy and polyploidy is that 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.[2]

Polyploidy may occur due to abnormal cell division, either during mitosis, or commonly during metaphase I in meiosis.

Polyploidy occurs in some animals, such as goldfish,[3] salmon, and salamanders, but is especially 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. Polyploidization is a mechanism of sympatric speciation because polyploids are usually unable to interbreed with their diploid ancestors.

Polyploidy 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 also will double the existing chromosome content.

Contents

Polyploid types

Polyploid types are labeled according to the number of chromosome sets in the nucleus:

Polyploidy in animals

Examples in animals are more common in the 'lower' forms[8] such as flatworms, leeches, and brine shrimp. Polyploid animals are often sterile, so they often reproduce by parthenogenesis. Polyploid lizards are also quite common and parthenogenetic. Polyploid mole salamanders (mostly triploids) are all female and reproduce by kleptogenesis,[9] "stealing" spermatophores from diploid males of related species to trigger egg development but not incorporating the males' DNA into the offspring. While mammalian liver cells are polyploid, 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'[10]. 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.[11] The 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 in humans

True polyploidy rarely occurs in humans, although it occurs in some tissues (especially in the liver). 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 miscarriage and those that do survive to term typically die shortly after birth. In some cases survival past birth may occur longer if there is mixoploidy with both a diploid and a triploid cell population present.

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.[12] 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 triploidy that survives into the fetal period.[citation needed] However, among early miscarriages, digyny is also more common in those cases <8.5 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.[citation needed] In diandry, a partial hydatidiform mole develops.[12] 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.

Polyploidy in plants

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

Polyploidy is pervasive in plants and some estimates suggest that 30–80% of living plant species are polyploid, and many lineages show evidence of ancient polyploidy (paleopolyploidy) in their genomes.[13][14][15] Huge explosions in angiosperm species diversity appear to have coincided with the timing of ancient genome duplications shared by many species.[16] It has been established that 15% of angiosperm and 31% of fern speciation events are accompanied by ploidy increase.[17] Polyploid plants can arise spontaneously in nature by several mechanisms, including meiotic or mitotic failures, and fusion of unreduced (2n) gametes.[18] Both autopolyploids (e.g. potato [19]) and allopolyploids (e.g. canola, wheat, cotton) can be found among both wild and domesticated plant species. Most polyploids display heterosis relative to their parental species, and may display novel variation or morphologies that may contribute to the processes of speciation and eco-niche exploitation.[18][14] 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 [20][21][22][23]. Many of these rapid changes may contribute to reproductive isolation and speciation.

Lomatia tasmanica is an extremely rare Tasmanian shrub which is triploid and sterile, and reproduction is entirely vegetative with all plants having the same genetic structure.

There are few naturally occurring polyploid conifers. One example is the giant tree Sequoia sempervirens or Coast Redwood which is a hexaploid (6x) with 66 chromosomes (2n = 6x = 66), although the origin is unclear.[24]

Polyploid crops

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 of polyploid crops

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

Polyploidy in fungi

Schematic phylogeny of the fungi. Red circles indicate polyploidy, blue squares indicate hybridization. From Albertin and Marullo, 2012[27]

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[27] 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 (i.e., hybrid speciation without a change in chromosome number) has been evidenced for some fungal species (e.g., the basidiomycota Microbotryum violaceum [34]).

Schematic phylogeny of the Chromalveolata. Red circles indicate polyploidy, blue squares indicate hybridization. From Albertin and Marullo, 2012[27]

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[35] leading to chimeric chromosomes[36] have been described, as well as more punctual genetic modifications such as gene loss.[37] The homoealleles of the allotetraploid yeast S. pastorianus show unequal contribution to the transcriptome.[38] Phenotypic diversification is also observed following polyploidization and/or hybridization in fungi,[39] producing the fuel for natural selection and subsequent adaptation and speciation.

Polyploidy in the Chromalveolata

Other eukaryotic taxa have experienced one or more polyploidization events during their evolutionary history (see Albertin and Marullo, 2012[27] for review). The oomycetes, which are non-true fungi members, contain several examples of paleopolyploid and polyploid species, such as within the Phytophthora genus [40]. Some species of brown algae (Fucales, Laminariales [41] and diatoms [42]) contain apparent polyploid genomes. In the Alveolata group, the remarkable species Paramecium tetraurelia underwent three successive rounds of whole-genome duplication [43] and established itself as a major model for paleopolyploid studies.

Terminology

Autopolyploidy

Autopolyploids are polyploids with multiple chromosome sets derived from a single species. Autopolyploids can arise from a spontaneous, naturally occurring genome doubling, like the potato [44]. Others might form following fusion of 2n gametes (unreduced gametes). Bananas and apples can be found as autotriploids. Autopolyploid plants typically display polysomic inheritance, and are therefore often infertile and propagated clonally perfect.

Allopolyploidy

Allopolyploids are polyploids with chromosomes derived from different species. Precisely it is the result of multiplying the chromosome number in an F1 hybrid. Triticale is an example of an allopolyploid, having six chromosome sets, allohexaploid, four from wheat (Triticum turgidum) and two from rye (Secale cereale). Amphidiploids are a type of allopolyploids (they are tetraploid, containing the diploid chromosome sets of both parents[45]). Some of the best examples of allopolyploids come from the Brassicas, and the Triangle of U describes the relationships among 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 diploids.

Paleopolyploidy

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

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 its other copy.

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 an early evolutionary ancestor of the vertebrates (which includes the human lineage) and another near the origin of the teleost fishes. Angiosperms (flowering plants) have paleopolyploidy in their ancestry. All eukaryotes probably have experienced a polyploidy event at some point in their evolutionary history.

Karyotype

A karyotype is the characteristic chromosome complement of a eukaryote species.[46][47] 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 karotypes, 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.

Paralogous

The term is used to describe the relationship among duplicated genes or portions of chromosomes that derived from a common ancestral DNA. Paralogous segments of DNA may arise spontaneously by errors during DNA replication, copy and paste transposons, or whole genome duplications.

Homologous

The term is used to describe the relationship of similar chromosomes that pair at mitosis and meiosis. In a diploid, one homolog is derived from the male parent (sperm) and one is derived from the female parent (egg). During meiosis and gametogenesis, homologous chromosomes pair and exchange genetic material by recombination, leading to the production of sperm or eggs with chromosome haplotypes containing novel genetic variation.

Homoeologous

The term homoeologous, also spelled homeologous, is used to describe the relationship of similar chromosomes or parts of chromosomes brought together following inter-species hybridization and allopolyploidization, and whose relationship was completely homologous in an ancestral species. In allopolyploids, the homologous chromosomes within each parental sub-genome should pair faithfully during meiosis, leading to disomic inheritance; however in some allopolyploids, the homoeologous chromosomes of the parental genomes may be nearly as similar to one another as the homologous chromosomes, leading to tetrasomic inheritance (four chromosomes pairing at meiosis), intergenomic recombination, and reduced fertility.

Example of homoeologous chromosomes

Durum wheat is the result of the inter-species hybridization of two diploid grass species Triticum urartu and Aegilops speltoides. Both the diploid ancestors had two sets of 7 chromosomes, which were similar in terms of size and genes contained on them. Durum wheat contains 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.

See also

References

  1. ^ Parmacek MS, Epstein JA (July 2009). "Cardiomyocyte renewal". N. Engl. J. Med. 361 (1): 86–8. doi:10.1056/NEJMcibr0903347. PMID 19571289. 
  2. ^ Griffiths, Anthony J. F. (1999). An Introduction to genetic analysis. San Francisco: W.H. Freeman. ISBN 0-7167-3520-2. 
  3. ^ 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. http://www.springerlink.com/content/n3rr5m124g728271/. 
  4. ^ Bertolani R (2001). "Evolution of the reproductive mechanisms in Tardigrades: a review". Zoologischer Anzeiger 240 (3-4): 247–252. doi:10.1078/0044-5231-00032. 
  5. ^ Wendel J. F. (2005). "Introduction to polyploid genome evolution and lessons from Gossypium". XVII International Botanical Congress. 
  6. ^ a b The genetic origin of kiwifruit. http://www.actahort.org/books/297/297_5.htm
  7. ^ Ainouche M. L., Fortune P. M., Salmon A., Parisod C., Grandbastien M. A., Fukunaga K., Ricou M., Misset M. T. (2009). "Hybridization, polyploidy and invasion: lessons from Spartina (Poaceae)". Biological Invasions 11: 1159-1173. doi:10.1007/s10530-008-9383-2. 
  8. ^ Otto S. P., Whitton J. (2000). "Polyploid incidence and evolution". Annu Rev Genet 34: 401-437. 
  9. ^ 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): 119–36. doi:10.1139/g06-152. PMID 17546077. 
  10. ^ Gallardo, M.H.; González, CA; Cebrián, I (2006), "Molecular cytogenetics and allotetraploidy in the red vizcacha rat, Tympanoctomys barrerae (Rodentia, Octodontidae)", Genomics 88 (2): 214–221, August 2006, doi:10.1016/j.ygeno.2006.02.010, PMID 16580173, http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WG1-4JKYTJP-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=a18e9e7ecd4f6082c8579d751043661d, retrieved 2008-07-16 
  11. ^ Svartman M, Stone G, Stanyon R (Aprilt 2005). "Molecular cytogenetics discards polyploidy in mammals". Genomics 85 (4): 425–30. doi:10.1016/j.ygeno.2004.12.004. PMID 15780745. 
  12. ^ a b Baker, Phil; Monga, Ash; Baker, Philip (2006). Gynaecology by ten teachers. London: Arnold. ISBN 0-340-81662-7. 
  13. ^ Meyers LA, Levin DA (June 2006). "On the abundance of polyploids in flowering plants". Evolution 60 (6): 1198–206. doi:10.1111/j.0014-3820.2006.tb01198.x. PMID 16892970. 
  14. ^ a b Rieseberg LH, Willis JH (August 2007). "Plant speciation". Science 317 (5840): 910–4. doi:10.1126/science.1137729. PMC 2442920. PMID 17702935. //www.ncbi.nlm.nih.gov/pmc/articles/PMC2442920/. 
  15. ^ Otto SP (November 2007). "The evolutionary consequences of polyploidy". Cell 131 (3): 452–62. doi:10.1016/j.cell.2007.10.022. PMID 17981114. 
  16. ^ De Bodt, S, Maere, S, Van de Peer, Y (2005). "Genome duplication and the origin of angiosperms". Trends Ecol. Evol. (Amst.) 20 (11): 591–7. doi:10.1016/j.tree.2005.07.008. PMID 16701441. 
  17. ^ Wood TE, Takebayashi N, Barker MS, Mayrose I, Greenspoon PB, Rieseberg LH (August 2009). "The frequency of polyploid speciation in vascular plants". Proc. Natl. Acad. Sci. U.S.A. 106 (33): 13875–9. doi:10.1073/pnas.0811575106. PMC 2728988. PMID 19667210. //www.ncbi.nlm.nih.gov/pmc/articles/PMC2728988/. 
  18. ^ a b Comai L (November 2005). "The advantages and disadvantages of being polyploid". Nat. Rev. Genet. 6 (11): 836–46. doi:10.1038/nrg1711. PMID 16304599. 
  19. ^ Consortium The Potato Genome Sequencing (2011). "Genome sequence and analysis of the tuber crop potato". Nature 475 (7355): 189-195. doi:10.1038/nature10158. 
  20. ^ Osborn TC, Pires JC, Birchler JA, Auger DL, Chen ZJ, Lee HS, Comai L, Madlung A, Doerge RW, Colot V, Martienssen RA (March 2003). "Understanding mechanisms of novel gene expression in polyploids". Trends Genet. 19 (3): 141–7. doi:10.1016/S0168-9525(03)00015-5. PMID 12615008. 
  21. ^ Chen ZJ, Ni Z (March 2006). "Mechanisms of genomic rearrangements and gene expression changes in plant polyploids". BioEssays 28 (3): 240–52. doi:10.1002/bies.20374. PMC 1986666. PMID 16479580. //www.ncbi.nlm.nih.gov/pmc/articles/PMC1986666/. 
  22. ^ Chen ZJ (2007). "Genetic and epigenetic mechanisms for gene expression and phenotypic variation in plant polyploids". Annu Rev Plant Biol 58: 377–406. doi:10.1146/annurev.arplant.58.032806.103835. PMC 1949485. PMID 17280525. //www.ncbi.nlm.nih.gov/pmc/articles/PMC1949485/. 
  23. ^ Albertin W., Balliau T., Brabant P., Chèvre A.-M., Eber F., Malosse C., Thiellement H. (2006). "Numerous and rapid non-stochastic modifications of gene products in newly synthesized Brassica napus allotetraploids". Genetics 173: 1101-1113. doi:10.1534/genetics.106.057554. 
  24. ^ 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. 
  25. ^ Seedless Fruits Make Others Needless
  26. ^ Emshwiller, E. (2006). "Origins of polyploid crops: The example of the octaploid tuber crop Oxalis tuberosa". In M.A. Zeder; D. Decker-Walters; E. Emshwiller; D. Bradley; B.D. Smith. Documenting domestication: new genetic and archaeological paradigms. Berkeley, USA: University of California Press. pp. 153–168. 
  27. ^ a b c d Albertin W., Marullo P. (2012). "Polyploidy in Fungi: evolution after whole-genome duplication". Proceedings of the Royal Society of London Series B-Biological Sciences In press. doi:10.1098/rspb.2012.0434. 
  28. ^ Emerson R., Wilson C. M. (1954). "Interspecific Hybrids and the Cytogenetics and Cytotaxonomy of Euallomyces". Mycologia 46: 393-434. 
  29. ^ Albertin W., Marullo P., Aigle M., Bourgais A., Bely M., Dillmann C., de Vienne D, Sicard D. (2009). "Evidence for autotetraploidy associated with reproductive isolation in Saccharomyces cerevisiae: towards a new domesticated species". J Evol Biol 22: 2157-70. doi:10.1111/j.1420-9101.2009.01828.x. 
  30. ^ Lu B. (1964). "Polyploidy in the Basidiomycete Cyathus stercoreus". Am J Bot 51: 343-347. 
  31. ^ Libkind D., Hittinger C. T., Valerio E., Goncalves C., Dover J., Johnston M., Goncalves P., Sampaio J. P. (2011). "Microbe domestication and the identification of the wild genetic stock of lager-brewing yeast". Proc Natl Acad Sci U S A 108: 14539-44. doi:10.1073/pnas.1105430108. 
  32. ^ Ma Li-Jun, Ibrahim Ashraf S., Skory Christopher, Grabherr Manfred G., Burger Gertraud, Butler Margi, Elias Marek, Idnurm Alexander, Lang B. Franz, Sone Teruo, Abe Ayumi, Calvo Sarah E., Corrochano Luis M., Engels Reinhard, Fu Jianmin, Hansberg Wilhelm, Kim Jung-Mi, Kodira Chinnappa D., Koehrsen Michael J., Liu Bo, Miranda-Saavedra Diego, O'Leary Sinead, Ortiz-Castellanos Lucila, Poulter Russell, Rodriguez-Romero Julio, Ruiz-Herrera José, Shen Yao-Qing, Zeng Qiandong, Galagan James, Birren Bruce W., Cuomo Christina A., Wickes Brian L. (2009). "Genomic Analysis of the Basal Lineage Fungus Rhizopus oryzae Reveals a Whole-Genome Duplication". PLoS Genet 5: e1000549. 
  33. ^ Wong S., Butler G., Wolfe K. H. (2002). "Gene order evolution and paleopolyploidy in hemiascomycete yeasts". Proc Natl Acad Sci U S A 99: 9272-7. doi:10.1073/pnas.142101099 142101099[pii]. 
  34. ^ Devier Benjamin, Aguileta Gabriela, Hood Michael E., Giraud Tatiana (2010). "Using phylogenies of pheromone receptor genes in the Microbotryum violaceum species complex to investigate possible speciation by hybridization". Mycologia 102: 689-696. doi:10.3852/09-192. 
  35. ^ Dunn B., Sherlock G. (2008). "Reconstruction of the genome origins and evolution of the hybrid lager yeast Saccharomyces pastorianus". Genome Res 18: 1610-23. doi:10.1101/gr.076075.108. 
  36. ^ Nakao Y., Kanamori T., Itoh T., Kodama Y., Rainieri S., Nakamura N., Shimonaga T., Hattori M., Ashikari T. (2009). "Genome sequence of the lager brewing yeast, an interspecies hybrid". DNA Res 16: 115-29. doi:10.1093/dnares/dsp003. PMC 2673734. PMID 19261625. //www.ncbi.nlm.nih.gov/pmc/articles/PMC2673734/. 
  37. ^ Scannell D. R., Byrne K. P., Gordon J. L., Wong S., Wolfe K. H. (2006). "Multiple rounds of speciation associated with reciprocal gene loss in polyploid yeasts". Nature 440: 341-5. doi:10.1038/nature04562. 
  38. ^ Minato T., Yoshida S., Ishiguro T., Shimada E., Mizutani S., Kobayashi O., Yoshimoto H. (2009). "Expression profiling of the bottom fermenting yeast Saccharomyces pastorianus orthologous genes using oligonucleotide microarrays". Yeast 26: 147-65. doi:10.1002/yea.1654. 
  39. ^ Lidzbarsky G. A., Shkolnik T., Nevo E. (2009). "Adaptive response to DNA-damaging agents in natural Saccharomyces cerevisiae populations from "Evolution Canyon", Mt. Carmel, Israel". PLoS ONE 4: e5914. doi:10.1371/journal.pone.0005914. 
  40. ^ Ioos Renaud, Andrieux Axelle, Marçais Benoît, Frey Pascal (2006). "Genetic characterization of the natural hybrid species Phytophthora alni as inferred from nuclear and mitochondrial DNA analyses". Fungal Genetics and Biology 43: 511-529. 
  41. ^ Phillips Naomi, Kapraun Donald F., GÃmez Garreta Amelia, Ribera Siguan Mª Antonia, Rull Jorde L., Salvador Soler Noemi, Lewis Raymond, Kawai Hiroshi (2011). "Estimates of nuclear DNA content in ninety eight species of brown algae (Phaeophyta)". AoB Plants. doi:10.1093/aobpla/plr001. 
  42. ^ Chepurnov V. A., Mann David G., Vyverman W., Sabbe K., Danielidis D. B. (2002). "SEXUAL REPRODUCTION, MATING SYSTEM, AND PROTOPLAST DYNAMICS OF SEMINAVIS (BACILLARIOPHYCEAE)". J Phycol 38: 1004-1019. 
  43. ^ Aury J. M., Jaillon O., Duret L., Noel B., Jubin C., Porcel B. M., Segurens B., Daubin V., Anthouard V., Aiach N., Arnaiz O., Billaut A., Beisson J., Blanc I., Bouhouche K., Camara F., Duharcourt S., Guigo R., Gogendeau D., Katinka M., Keller A. M., Kissmehl R., Klotz C., Koll F., Le Mouel A., Lepere G., Malinsky S., Nowacki M., Nowak J. K., Plattner H., Poulain J., Ruiz F., Serrano V., Zagulski M., Dessen P., Betermier M., Weissenbach J., Scarpelli C., Schachter V., Sperling L., Meyer E., Cohen J., Wincker P. (2006). "Global trends of whole-genome duplications revealed by the ciliate Paramecium tetraurelia". Nature 444 (7116): 171-8. doi:10.1038/nature05230. PMID 17086204. 
  44. ^ Consortium The Potato Genome Sequencing (2011). "Genome sequence and analysis of the tuber crop potato". Nature 475 (7355): 189-195. doi:10.1038/nature10158. 
  45. ^ Rieger, R.; Michaelis, A.; Green, M.M. (1968). A glossary of genetics and cytogenetics: Classical and molecular. 
  46. ^ White M.J.D. 1973. The chromosomes. 6th ed, Chapman & Hall, London. p28
  47. ^ Stebbins G.L. 1950. Variation and evolution in plants. Chapter XII: The Karyotype. Columbia University Press N.Y.

Further reading

External links