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Polyploidy is a condition in which the
cell
cell
s of an
organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological me ...

organism
have more than two paired ( homologous) sets of
chromosome A chromosome is a long DNA molecule with part or all of the genome, genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by Chaperone (protein), chaperone proteins, bind to and ...

chromosome
s. Most species whose cells have
nuclei ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA ...

nuclei
(
eukaryotes Eukaryotes () are organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It is a synonym for "Outline ...
) are
diploid Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal genes. Sets of chromosomes refer to the number of mate ...
, meaning they have two sets of chromosomes—one set inherited from each parent. However, some organisms are polyploid. Polyploidy is especially common in plants. Most eukaryotes have diploid
somatic cells A somatic cell (from Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following period ...
, but produce
haploid Ploidy () is the number of complete sets of chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by ...
gametes A gamete ( /ˈɡæmiːt/; from Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the foll ...
(eggs and sperm) by
meiosis Meiosis (; , because it is a reductional division) is a special type of of in organisms used to produce the , such as or . It involves two rounds of division that ultimately result in four cells with only one copy of each (). Additionall ...

meiosis
. A
monoploid Ploidy () is the number of complete sets of chromosome A chromosome is a long DNA The structure of part of a DNA double helix Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling ...
has only one set of chromosomes, and the term is usually only applied to cells or organisms that are normally haploid. Males of
bee Bees are flying insects closely related to wasps and ants, known for their role in pollination and, in the case of the best-known bee species, the western honey bee, for producing honey. Bees are a monophyly, monophyletic lineage within the ...

bee
s and other
Hymenoptera Hymenoptera is a large order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, dirt, trash, or wa ...

Hymenoptera
, for example, are monoploid. Unlike animals,
plants Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cellular respiration, can later be released to fuel t ...

plants
and multicellular
algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic Photosynthesis is a process used by plants and other organisms to convert Conversion or convert may refer to: Arts, entertainment, and media * Co ...

algae
have
life cycle Life cycle, life-cycle, or lifecycle may refer to: Science and academia *Biological life cycle, the sequence of life stages that an organism undergoes from birth to reproduction ending with the production of the offspring *Life-cycle hypothesis, ...
s with two
alternating multicellular generations
alternating multicellular generations
. The
gametophyte A gametophyte () is one of the two alternating multicellular phases in the life cycles of plant Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all ...
generation is haploid, and produces gametes by
mitosis In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical proce ...

mitosis
, the
sporophyte 350px, Sporophytes of moss during spring A sporophyte () is the diploid Ploidy () is the number of complete sets of chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryo ...
generation is diploid and produces
spores In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mecha ...
by
meiosis Meiosis (; , because it is a reductional division) is a special type of of in organisms used to produce the , such as or . It involves two rounds of division that ultimately result in four cells with only one copy of each (). Additionall ...

meiosis
. Polyploidy may occur due to abnormal
cell division Cell division is the process by which a parent cell (biology), cell divides into two or more daughter cells. Cell division usually occurs as part of a larger cell cycle. In eukaryotes, there are two distinct types of cell division; a vegetative ...

cell division
, either during mitosis, or commonly during
metaphase I spermatocyte, played back at 120× the recorded speed Meiosis (; from Greek language, Greek μείωσις, ''meiosis'', meaning "lessening") is a special type of cell division Cell division is the process by which a parent Cell (biology), ...
in meiosis(it may arise from the failure of chromosomes to separate during meiosis or from the fertilization of an egg by more than one sperm). In addition, it can be induced in plants and
cell culture Cell culture is the process by which cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or religious recluse ...

cell culture
s by some chemicals: the best known is
colchicine Colchicine is a medication used to treat and . In gout, it is less preferred to s or . Other uses for colchicine include the management of and . Colchicine is taken by mouth. Colchicine has a narrow , so overdosing is a significant risk. Co ...

colchicine
, which can result in chromosome doubling, though its use may have other less obvious consequences as well.
Oryzalin Oryzalin is an herbicide of the dinitroaniline class. It acts through the disruption (depolymerization) of microtubules, thus blocking Anisotropy, anisotropic growth of plant cells. It can also be used to induce Polyploid, polyploidy in plants as ...

Oryzalin
will also double the existing chromosome content. Polyploidy occurs in highly differentiated human tissues in the liver, heart muscle, bone marrow and the placenta. It occurs in the somatic cells of some
animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells ...

animal
s, such as
goldfish The goldfish (''Carassius auratus'') is a freshwater fish are common freshwater fish throughout temperate Eurasia. Freshwater fish are those that spend some or all of their lives in fresh water, such as river A river is a natural flowi ...

goldfish
,
salmon Salmon is the common name for several species of ray-finned fish Actinopterygii ( New Latin ('having rays') + Greek ( 'wing, fins')), members of which are known as ray-finned fishes, is a clade A clade (; from grc, , ''klados'', ...

salmon
, and
salamander Salamanders are a group of amphibian Amphibians are ectothermic, tetrapod vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most spe ...

salamander
s, but is especially common among
fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plant Vascular plants (from Latin ''vasculum'': duct), also known as Tracheophyta (the tracheophytes , from Greek τραχεῖα ἀρτηρία ''trācheia art ...

fern
s and flowering
plant Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cellular respiration, can later be released to fuel ...

plant
s (see ''
Hibiscus rosa-sinensis ''Hibiscus rosa-sinensis'', known colloquially as Chinese hibiscus, China rose, Hawaiian hibiscus, rose mallow and shoeblack plant, is a of tropical hibiscus, a in the of the Malvaceae. It is widely cultivated in tropical and subtropical re ...

Hibiscus rosa-sinensis
''), including both wild and cultivated
species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...

species
.
Wheat Wheat is a grass widely cultivated for its seed, a cereal grain which is a worldwide staple food. The many species of wheat together make up the genus ''Triticum''; the most widely grown is common wheat Common wheat (''Triticum aestivum'' ...

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 Durum wheat (), also called pasta wheat or macaroni wheat (''Triticum durum'' or ''Triticum turgidum'' subsp. ''durum''), is a species of . It is the second most cultivated species of wheat after , although it represents only 5% to 8% of global ...
or macaroni wheat, and hexaploid (six sets of chromosomes) with the common name of bread wheat. Many agriculturally important plants of the genus ''
Brassica ''Brassica'' () is a genus of plants in the cabbage and mustard Mustard may refer to: Food and plants * Mustard (condiment) Mustard is a condiment made from the seeds A seed is an Plant embryogenesis, embryonic plant enclosed in a te ...
'' are also tetraploids.
Sugarcane Sugarcane or sugar cane is a species of (often hybrid) tall, perennial A perennial plant or simply perennial is a plant Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, ...

Sugarcane
can have ploidy levels higher than octaploid. Polyploidization can be a mechanism of 
sympatric speciation Sympatric speciation is the evolution of a new species from a surviving ancestral species while both continue to inhabit the same geographic region. In evolutionary biology and biogeography, sympatric and sympatry are terms referring to organisms ...
 because polyploids are usually unable to interbreed with their diploid ancestors. An example is the plant ''
Erythranthe peregrina ''Erythranthe peregrina'' is a species of monkeyflower. Its Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, kn ...

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 The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' use Britain as a synonym for the United Kingdom. Some prefer to use Britain as shorth ...

United Kingdom
. New populations of ''E. peregrina'' arose on
the Scottish mainland
the Scottish mainland
and the
Orkney Islands Orkney (; sco, Orkney; on, Orkneyjar; nrn, Orknøjar), also known as the Orkney Islands, is an archipelago in the Northern Isles of Scotland, situated off the north coast of the island of Great Britain. Orkney is 10 miles (16 km) north ...

Orkney Islands
via genome duplication from local populations of ''E. × robertsii''. Because of a rare genetic mutation, ''E. peregrina'' is not sterile.


Terminology


Types

Polyploid types are labeled according to the number of chromosome sets in the
nucleus ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA ...

nucleus
. The letter ''x'' is used to represent the number of chromosomes in a single set: *haploid (one set; 1x) *diploid (two sets; 2x) *triploid (three sets; 3''x''), for example sterile saffron crocus, or seedless watermelons, also common in the
phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number. The plural of a noun typically denotes a q ...
Tardigrada Tardigrades (), known colloquially as water bears or moss piglets, are a phylum of eight-legged segmented micro-animals. They were first described by the German zoologist Johann August Ephraim Goeze in 1773, who called them little water bears ...
*tetraploid (four sets; 4''x''), for example
Salmonidae Salmonidae is a Family (biology), family of ray-finned fish, the only living family currently placed in the Order (biology), order Salmoniformes . It includes salmon (both ocean-going and lake-locked), trout, Salvelinus, chars, freshwater whitef ...
fish, the cotton ''
Gossypium hirsutum ''Gossypium hirsutum'', also known as upland cotton or Mexican cotton, is the most widely planted species of cotton in the world. Globally, about 90% of all cotton production is of cultivars derived from this species. In the United States ...

Gossypium hirsutum
'' *pentaploid (five sets; 5''x''), for example Kenai Birch (''
Betula kenaica ''Betula kenaica'', or Kenai birch, is a species of birch A birch is a thin-leaved deciduous hardwood tree of the genus ''Betula'' (), in the family Betulaceae, which also includes alders, hazels, and hornbeams. It is closely related to the be ...
'') *hexaploid (six sets; 6''x''), for example
wheat Wheat is a grass widely cultivated for its seed, a cereal grain which is a worldwide staple food. The many species of wheat together make up the genus ''Triticum''; the most widely grown is common wheat Common wheat (''Triticum aestivum'' ...

wheat
,
kiwifruit A sliced kiwifruit Kiwifruit (often shortened to kiwi in North America and Euro English, continental Europe) or Chinese gooseberry is the edible berry (botany), berry of several species of woody plant, woody vines in the genus ''Actinidia''. Th ...

kiwifruit
*heptaploid or septaploid (seven sets; 7''x'') *octaploid or octoploid, (eight sets; 8''x''), for example ''
Acipenser ''Acipenser'' is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a ...
'' (genus of
sturgeon Sturgeon is the common name Common may refer to: Places * Common, a townland in County Tyrone, Northern Ireland * Boston Common Boston Common (also known as the Common) is a central public park in downtown Boston, Massachusetts. It is s ...

sturgeon
fish),
dahlia Dahlia ( or ) is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology Biology is the natural science that studies life and living organisms, including the ...

dahlia
s *decaploid (ten sets; 10''x''), for example certain
strawberries The garden strawberry (or simply strawberry; ''Fragaria × ananassa'') is a widely grown Hybrid (biology), hybrid species of the genus ''Fragaria'', collectively known as the strawberries, which are cultivated worldwide for their fruit. The f ...

strawberries
*dodecaploid or duodecaploid (twelve sets; 12''x''), for example the plants ''
Celosia argentea ''Celosia argentea'', commonly known as the plumed cockscomb or silver cock's comb, is a herb In general use, herbs are plants with savory or aromatic properties that are used for flavoring and garnishing food, for medicinal purposes, or for f ...

Celosia argentea
'' and ''
Spartina anglica
Spartina anglica
'' or the amphibian '' Xenopus ruwenzoriensis''.


Classification


Autopolyploidy

Autopolyploids are polyploids with multiple chromosome sets derived from a single
taxon In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechani ...
. Two examples of natural autopolyploids are the piggyback plant, ''
Tolmiea menzisii
Tolmiea menzisii
'' and the white sturgeon, '' Acipenser transmontanum''. Most instances of autopolyploidy result from the fusion of unreduced (2''n'') gametes, which results in either triploid (''n'' + 2''n'' = 3''n'') or tetraploid (2''n'' + 2''n'' = 4''n'') offspring. 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”. Triploids may also persist through
asexual reproduction Asexual reproduction is a type of reproduction Reproduction (or procreation or breeding) is the biological process Biological processes are those processes that are vital for an organism In biology, an organism (from Ancient Gree ...
. In fact, stable autotriploidy in plants is often associated with
apomictic In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Anc ...
mating systems. In agricultural systems, autotriploidy can result in seedlessness, as in
watermelon Watermelon (''Citrullus lanatus'') is a flowering plant Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek Greek may refer to: Greece Any ...

watermelon
s and
banana A banana is an elongated, edible fruit In botany, a fruit is the seed-bearing structure in flowering plants (also known as angiosperms) formed from the ovary after flowering. Fruits are the means by which angiosperms dissemin ...

banana
s. Triploidy is also utilized in salmon and trout farming to induce sterility. Rarely, autopolyploids arise from spontaneous, somatic genome doubling, which has been observed in apple (''Malus domesticus'') bud sports. This is also the most common pathway of artificially induced polyploidy, where methods such as
protoplast fusion Somatic fusion, also called protoplast fusion, is a type of genetic modification in plants by which two distinct species of plants are fused together to form a new Hybrid (biology), hybrid plant with the characteristics of both, a somatic hybrid. ...
or treatment with
colchicine Colchicine is a medication used to treat and . In gout, it is less preferred to s or . Other uses for colchicine include the management of and . Colchicine is taken by mouth. Colchicine has a narrow , so overdosing is a significant risk. Co ...

colchicine
,
oryzalin Oryzalin is an herbicide of the dinitroaniline class. It acts through the disruption (depolymerization) of microtubules, thus blocking Anisotropy, anisotropic growth of plant cells. It can also be used to induce Polyploid, polyploidy in plants as ...

oryzalin
or
mitotic inhibitor , a widely used mitotic inhibitor. A mitotic inhibitor is a drug that inhibits mitosis In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division gives rise to gene ...
s are used to disrupt normal
mitotic In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. In gene ...

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. Autopolyploids possess at least three
homologous chromosome A couple of homologous chromosomes, or homologs, are a set of one maternal and one paternal chromosome A chromosome is a long DNA The structure of part of a DNA double helix Deoxyribonucleic acid (; DNA) is a molecule File:Pen ...
sets, which can lead to high rates of multivalent pairing during
meiosis Meiosis (; , because it is a reductional division) is a special type of of in organisms used to produce the , such as or . It involves two rounds of division that ultimately result in four cells with only one copy of each (). Additionall ...

meiosis
(particularly in recently formed autopolyploids, also known as neopolyploids) and an associated decrease in fertility due to the production of
aneuploid Aneuploidy is the presence of an abnormal number of chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aid ...
gametes. Natural or artificial selection for fertility can quickly stabilize meiosis in autopolyploids by restoring bivalent pairing during meiosis, but the high degree of homology among duplicated chromosomes causes autopolyploids to display polysomic inheritance. 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. 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. About half of all polyploids are thought to be the result of autopolyploidy, although many factors make this proportion hard to estimate.


Allopolyploidy

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 (2''n'') gametes, which can take place before or after hybridization. In the former case, unreduced gametes from each diploid taxa – 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. 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
nondisjunctionNondisjunction is the failure of homologous chromosomes or sister chromatids 300px, The paternal (blue) chromosome and the maternal (pink) chromosome are homologous chromosomes. Following chromosomal DNA replication, the blue chromosome is compose ...
during meiosis. In this case, allopolyploidy can actually restore normal,
bivalentBivalent may refer to: * Bivalent (chemistry), a molecule formed from two or more atoms bound together *Bivalent (engine), an engine that can operate on two different types of fuel *Bivalent (genetics), a pair of homologous chromosomes *Bivalent logi ...
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. Because pairing between homoeologous chromosomes is rare in established allopolyploids, they may benefit from fixed
heterozygosity Zygosity (the noun, zygote A zygote (from Greek ζυγωτός ''zygōtos'' "joined" or "yoked", from ζυγοῦν ''zygoun'' "to join" or "to yoke") is a eukaryotic cell formed by a fertilization event between two gamete A gamete ( /ˈ ...
of homoeologous alleles. In certain cases, such heterozygosity can have beneficial 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 Wheat is a grass widely cultivated for its seed, a cereal grain which is a worldwide staple food. The many species of wheat together make up the genus ''Triticum''; the most widely grown is common wheat Common wheat (''Triticum aestivum'' ...

wheat
and ''
Triticale Triticale (; × ''Triticosecale'') is a hybrid of wheat Wheat is a grass widely Agriculture, cultivated for its seed, a cereal grain which is a worldwide staple food. The Taxonomy of wheat, many species of wheat together make up the genus ''Tr ...

Triticale
'' are examples of an allopolyploids with six chromosome sets.
Cotton Cotton is a soft, fluffy staple fiber Fiber or fibre (from la, fibra, links=no) is a natural Nature, in the broadest sense, is the natural, physical, material world or universe The universe ( la, universus) is all of s ...

Cotton
,
peanut The peanut, also known as the groundnut, goober (US), pindar (US) or monkey nut (UK), and taxonomically classified as ''Arachis hypogaea'', is a legume A legume () is a plant Plants are predominantly photosynthetic Photosynth ...

peanut
, or
quinoa Quinoa (''Chenopodium quinoa''; , from Quechua Quechua may refer to: *Quechua people, several indigenous ethnic groups in South America, especially in Peru *Quechuan languages, a Native South American language family spoken primarily in the ...

quinoa
are allotetraploids with multiple origins. In Brassicaceous crops, the
Triangle of U The triangle of U ( ) is a theory about the evolution and relationships among members of the plant genus ''Brassica''. The theory states that the genomes of three ancestral diploid species of ''Brassica'' combined to create three common tetraploid v ...
describes the relationships between the three common diploid Brassicas ('', ,'' and '''') and three allotetraploids ('',
B. juncea ''B. juncea'' may refer to: * ''Baccharis juncea'', a New World plant * ''Baumea juncea'', a rhizomatous herb * ''Bebbia juncea'', an aromatic shrub * ''Belonogaster juncea'', a paper wasp * ''Bouteloua juncea'', a true grass * ''Brassica juncea'', ...

B. juncea
,'' and '' B. carinata'') derived from hybridization among the diploid species. A similar relationship exists between three diploid species of ''
Tragopogon ''Tragopogon'', also known as goatsbeard or salsify, is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such clas ...

Tragopogon
'' ('', ,'' and '' T. porrifolius'') and two allotetraploid species (''Tragopogon mirus, T. mirus'' and ''Tragopogon miscellus, T. miscellus''). Complex patterns of allopolyploid evolution have also been observed in animals, as in the frog genus ''Xenopus.''


Aneuploid

Organisms in which a particular chromosome, or chromosome segment, is under- or over-represented are said to be
aneuploid Aneuploidy is the presence of an abnormal number of chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aid ...
(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.


Endopolyploidy

Polyploidy occurs in some tissues of animals that are otherwise diploid, such as human muscle tissues. 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''. Hence ploidy is defined with respect to a cell.


Monoploid

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 Ploidy () is the number of complete sets of chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by ...
.


Temporal terms


Neopolyploidy

A polyploid that is newly formed.


Mesopolyploidy

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

Ancient genome duplications probably occurred in the evolutionary history of all life. Duplication events that occurred long ago in the history of various Lineage (evolution), 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. In many cases, these events can be inferred only through comparing DNA sequencing, 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.


Other similar terms


Karyotype

A karyotype is the characteristic chromosome complement of a eukaryote
species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...

species
. The preparation and study of karyotypes is part of cytopathology, cytology and, more specifically, cytogenetics. Although the replication and transcription of DNA is highly standardized in
eukaryotes Eukaryotes () are organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It is a synonym for "Outline ...
, 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

Homoeologous chromosomes are those brought together following Hybrid (biology), inter-species hybridization and Allopolyploidy, allopolyploidization, and whose relationship was completely homologous in an ancestral species. For example, Durum#Genealogy, 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 Eukaryote hybrid genome, 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


Animals

Examples in animals are more common in non-vertebrates such as flatworms, leeches, and brine shrimp. Within vertebrates, examples of stable polyploidy include the salmonids and many cyprinids (i.e. carp). Some fish have as many as 400 chromosomes. 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). Polyploid lizards are also quite common. Most are sterile and reproduce by parthenogenesis; others, like ''Liolaemus chiliensis'', maintain sexual reproduction. Polyploid mole salamanders (mostly triploids) are all female and reproduce by kleptogenesis, "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 Octodontidae, 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'. 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. This rodent is not a rat, but kin to guinea pigs and chinchillas. Its "new" diploid (2''n'') number is 102 and so its cells are roughly twice normal size. Its closest living relation is ''Octomys mimax'', the Andes, Andean Viscacha-Rat of the same family, whose 2''n'' = 56. It was therefore surmised that an ''Octomys''-like ancestor produced tetraploid (i.e., 2''n'' = 4''x'' = 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. Cold or heat shock has also been shown to result in unreduced amphibian gametes, though this occurs more commonly in eggs than in sperm. 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. 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 "Cloning, 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.


Humans

True polyploidy rarely occurs in humans, although polyploid cells occur in highly Cellular differentiation, differentiated tissue, such as liver parenchyma, heart muscle, placenta and in bone marrow. Aneuploidy is more common. Polyploidy occurs in humans in the form of Triploid syndrome, 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. 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 Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal genes. Sets of chromosomes refer to the number of mate ...
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. 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. 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. However, among early miscarriages, digyny is also more common in those cases less than 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 Ploidy () is the number of complete sets of chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by ...
set. In digyny, there is typically an asymmetric poorly grown fetus, with marked adrenal hypoplasia and a very small placenta. In diandry, a partial hydatidiform mole develops. These parent-of-origin effects reflect the effects of imprinting (genetics), genomic imprinting. 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.


Fishes

A polyploidy event occurred within the stem lineage of the teleost fishes.


Plants

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. Huge explosions in angiosperm species diversity appear to have coincided with the timing of ancient genome duplications shared by many species. It has been established that 15% of angiosperm and 31% of fern speciation events are accompanied by ploidy increase. Polyploid plants can arise spontaneously in nature by several mechanisms, including meiotic or mitotic failures, and fusion of unreduced (2''n'') gametes. Both autopolyploids (e.g. potato) 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. 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. Many of these rapid changes may contribute to reproductive isolation and speciation. However seed generated from interploidy hybridization, interploidy crosses, such as between polyploids and their parent species, usually suffer from aberrant endosperm development which impairs their viability, thus contributing to polyploid speciation. Some plants are triploid. As
meiosis Meiosis (; , because it is a reductional division) is a special type of of in organisms used to produce the , such as or . It involves two rounds of division that ultimately result in four cells with only one copy of each (). Additionall ...

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. One example is the Coast Redwood ''Sequoia sempervirens'', which is a hexaploid (6''x'') with 66 chromosomes (2''n'' = 6''x'' = 66), although the origin is unclear. Aquatic plants, especially the Monocotyledons, include a large number of polyploids.


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 Wheat is a grass widely cultivated for its seed, a cereal grain which is a worldwide staple food. The many species of wheat together make up the genus ''Triticum''; the most widely grown is common wheat Common wheat (''Triticum aestivum'' ...

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#Botanical use, colchicine.


= Examples

= * Triploid crops: some apple varieties (such as Belle de Boskoop, Jonagold, Mutsu (apple), Mutsu, Ribston Pippin),
banana A banana is an elongated, edible fruit In botany, a fruit is the seed-bearing structure in flowering plants (also known as angiosperms) formed from the ovary after flowering. Fruits are the means by which angiosperms dissemin ...

banana
, citrus, ginger,
watermelon Watermelon (''Citrullus lanatus'') is a flowering plant Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek Greek may refer to: Greece Any ...

watermelon
, saffron crocus, white pulp of coconut * Tetraploid crops: very few apple varieties,
durum Durum wheat (), also called pasta wheat or macaroni wheat (''Triticum durum'' or ''Triticum turgidum'' subsp. ''durum''), is a species of . It is the second most cultivated species of wheat after , although it represents only 5% to 8% of global ...
or macaroni
wheat Wheat is a grass widely cultivated for its seed, a cereal grain which is a worldwide staple food. The many species of wheat together make up the genus ''Triticum''; the most widely grown is common wheat Common wheat (''Triticum aestivum'' ...

wheat
, cotton, potato, canola/rapeseed, leek, tobacco,
peanut The peanut, also known as the groundnut, goober (US), pindar (US) or monkey nut (UK), and taxonomically classified as ''Arachis hypogaea'', is a legume A legume () is a plant Plants are predominantly photosynthetic Photosynth ...

peanut
, kinnow, Pelargonium * Hexaploid crops: chrysanthemum, bread
wheat Wheat is a grass widely cultivated for its seed, a cereal grain which is a worldwide staple food. The many species of wheat together make up the genus ''Triticum''; the most widely grown is common wheat Common wheat (''Triticum aestivum'' ...

wheat
, triticale, oat,
kiwifruit A sliced kiwifruit Kiwifruit (often shortened to kiwi in North America and Euro English, continental Europe) or Chinese gooseberry is the edible berry (botany), berry of several species of woody plant, woody vines in the genus ''Actinidia''. Th ...

kiwifruit
* Octaploid crops: strawberry,
dahlia Dahlia ( or ) is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology Biology is the natural science that studies life and living organisms, including the ...

dahlia
, pansies, sugar cane, oca (''Oxalis tuberosa'') * Dodecaploid crops: some sugar cane hybrids Some crops are found in a variety of ploidies: tulips and lily, lilies are commonly found as both diploid and triploid; daylilies (''Hemerocallis'' cultivars) are available as either diploid or tetraploid; apples and kinnow, kinnow mandarins can be diploid, triploid, or tetraploid.


Fungi

Besides plants and animals, the evolutionary history of various Fungus, fungal species is dotted by past and recent whole-genome duplication events (see Albertin and Marullo 2012 for review). Several examples of polyploids are known: *autopolyploid: the aquatic fungi of genus ''Allomyces'', some ''Saccharomyces cerevisiae'' strains used in bakery, etc. *allopolyploid: the widespread ''Cyathus stercoreus'', the allotetraploid lager yeast ''Saccharomyces pastorianus'', the allotriploid wine spoilage yeast ''Dekkera bruxellensis'', etc. *paleopolyploid: the human pathogen ''Rhizopus oryzae'', the genus ''Saccharomyces'', etc. In addition, polyploidy is frequently associated with hybridization and reticulate evolution that appear to be highly prevalent in several fungal taxa. Indeed, Hybrid speciation, homoploid speciation (hybrid speciation without a change in
chromosome A chromosome is a long DNA molecule with part or all of the genome, genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by Chaperone (protein), chaperone proteins, bind to and ...

chromosome
number) has been evidenced for some fungal species (such as the basidiomycota ''Microbotryum violaceum''). 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 leading to Chimera (genetics), chimeric chromosomes have been described, as well as more punctual genetic modifications such as gene loss. The homoealleles of the allotetraploid yeast ''S. pastorianus'' show unequal contribution to the transcriptome. Phenotypic diversification is also observed following polyploidization and/or hybridization in fungi, producing the fuel for natural selection and subsequent adaptation and speciation.


Chromalveolata

Other eukaryotic taxon, taxa have experienced one or more polyploidization events during their evolutionary history (see Albertin and Marullo, 2012 for review). The oomycetes, which are non-true fungi members, contain several examples of paleopolyploid and polyploid species, such as within the genus ''Phytophthora''. Some species of brown
algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic Photosynthesis is a process used by plants and other organisms to convert Conversion or convert may refer to: Arts, entertainment, and media * Co ...

algae
(Fucales, Laminariales and diatoms) contain apparent polyploid genomes. In the Alveolata group, the remarkable species ''Paramecium tetraurelia'' underwent three successive rounds of whole-genome duplication and established itself as a major model for paleopolyploid studies.


Bacteria

Each ''Deinococcus radiodurans'' bacteria, bacterium contains 4-8 copies of its
chromosome A chromosome is a long DNA molecule with part or all of the genome, genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by Chaperone (protein), chaperone proteins, bind to and ...

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


Archaea

The archaea, archaeon ''Halobacterium salinarium'' is polyploid and, like ''Deinococcus radiodurans'', is highly resistant to X-ray irradiation and desiccation, conditions that induce DNA double-strand breaks. 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.


See also

*Eukaryote hybrid genome * Polyploid complex * Polysomy * Sympatry *Diploidization *Ploidy


References


Further reading

* * * * * * * * * * * * * * * * * *


External links


Polyploidy on Kimball's Biology Pages

The polyploidy portal
a community-editable project with information, research, education, and a bibliography about polyploidy. {{Authority control Classical genetics Speciation he:פלואידיות#פוליפלואידיות fi:Ploidia#Polyploidia sv:Ploiditet#Polyploiditet