![Haploid, diploid ,triploid and tetraploid](https://upload.wikimedia.org/wikipedia/commons/a/aa/Haploid%2C_diploid_%2Ctriploid_and_tetraploid.svg)
Polyploidy is a condition in which the
cell
Cell most often refers to:
* Cell (biology), the functional basic unit of life
Cell may also refer to:
Locations
* Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery ...
s of an
organism
In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...
have more than one pair of (
homologous)
chromosome
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
s. Most species whose cells have
nuclei (
eukaryotes) are
diploid, meaning they have two sets of chromosomes, where each set contains one or more chromosomes and comes from each of two parents, resulting in pairs of homologous chromosomes between sets. However, some organisms are polyploid. Polyploidy is especially common in plants. Most eukaryotes have diploid
somatic cells
A somatic cell (from Ancient Greek σῶμα ''sôma'', meaning "body"), or vegetal cell, is any biological cell forming the body of a multicellular organism other than a gamete, germ cell, gametocyte or undifferentiated stem cell. Such cells compo ...
, but produce
haploid gametes
A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...
(eggs and sperm) by
meiosis
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...
. A
monoploid
Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respective ...
has only one set of chromosomes, and the term is usually only applied to cells or organisms that are normally diploid. Males of
bees and other
Hymenoptera
Hymenoptera is a large order (biology), order of insects, comprising the sawfly, sawflies, wasps, bees, and ants. Over 150,000 living species of Hymenoptera have been described, in addition to over 2,000 extinct ones. Many of the species are Par ...
, for example, are monoploid. Unlike animals,
plants
Plants are predominantly Photosynthesis, photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all curr ...
and multicellular
algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
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. The
gametophyte
A gametophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has on ...
generation is haploid, and produces gametes by
mitosis
In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis gives rise to genetically identical cells in which the total number of chromosomes is mainta ...
, the
sporophyte
A sporophyte () is the diploid multicellular stage in the life cycle of a plant or alga which produces asexual spores. This stage alternates with a multicellular haploid gametophyte phase.
Life cycle
The sporophyte develops from the zygote pr ...
generation is diploid and produces
spores
In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...
by
meiosis
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...
.
Polyploidy may occur due to abnormal
cell division
Cell division is the process by which a parent cell (biology), cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukar ...
, 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. In addition, it can be induced in plants and
cell culture
Cell culture or tissue culture is the process by which cells are grown under controlled conditions, generally outside of their natural environment. The term "tissue culture" was coined by American pathologist Montrose Thomas Burrows. This te ...
s by some chemicals: the best known is
colchicine
Colchicine is a medication used to treat gout and Behçet's disease. In gout, it is less preferred to NSAIDs or steroids. Other uses for colchicine include the management of pericarditis and familial Mediterranean fever. Colchicine is taken b ...
, 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 anisotropic growth of plant cells. It can also be used to induce polyploid
Polyploidy is a condition in w ...
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 are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
s, such as
goldfish
The goldfish (''Carassius auratus'') is a freshwater fish in the family Cyprinidae of order Cypriniformes. It is commonly kept as a pet in indoor aquariums, and is one of the most popular aquarium fish. Goldfish released into the wild have bec ...
,
salmon
Salmon () is the common name for several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the family (biology), family Salmonidae, which are native to tributary, tributaries of the ...
, and
salamander
Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All ten ...
s, but is especially common among
fern
A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except t ...
s and flowering
plant
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...
s (see ''
Hibiscus rosa-sinensis
''Hibiscus rosa-sinensis'', known colloquially as Chinese hibiscus, China rose, Hawaiian hibiscus, rose mallow and shoeblack plant, is a species of tropical hibiscus, a flowering plant in the Hibisceae Tribe (biology), tribe of the family (biol ...
''), including both wild and cultivated
species
In biology, a species is the basic unit of 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 individuals of the appropriate s ...
.
Wheat
Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...
, 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 tetraploid species of wheat. It is the second most cultivated species of wheat after common wheat, although it represen ...
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 family (Brassicaceae). The members of the genus are informally known as cruciferous vegetables, cabbages, or mustard plants. Crops from this genus are sometimes called ''cole cr ...
'' are also tetraploids.
Sugarcane
Sugarcane or sugar cane is a species of (often hybrid) tall, Perennial plant, perennial grass (in the genus ''Saccharum'', tribe Andropogoneae) that is used for sugar Sugar industry, production. The plants are 2–6 m (6–20 ft) tall with ...
can have ploidy levels higher than octaploid.
Polyploidization can be a mechanism of
sympatric speciation because polyploids are usually unable to interbreed with their diploid ancestors. An example is the plant ''
Erythranthe peregrina
''Erythranthe peregrina'' is a species of Erythranthe, monkeyflower. Its botanical Latin, Latin name means "foreign", or more loosely "the foreigner". This species is a rare example of Polyploid#Polyploidization and speciation, polyploidization a ...
''. 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, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
. New populations of ''E. peregrina'' arose on
the Scottish mainland and the
Orkney Islands via genome duplication from local populations of ''E. × robertsii''. Because of a rare genetic mutation, ''E. peregrina'' is not sterile.
Terminology
Types
![Organ-specific patterns of endopolyploidy in the giant ant Dinoponera australis - JHR-037-113-g001](https://upload.wikimedia.org/wikipedia/commons/6/65/Organ-specific_patterns_of_endopolyploidy_in_the_giant_ant_Dinoponera_australis_-_JHR-037-113-g001.jpg)
Polyploid types are labeled according to the number of chromosome sets in the
nucleus
Nucleus ( : 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
Nucl ...
. 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
''Crocus sativus'', commonly known as saffron crocus or autumn crocus, is a species of flowering plant in the iris family (biology), family Iridaceae. A cormous autumn-flowering cultivated perennial plant, perennial, unknown in the wild, it is ...
, or
seedless watermelons, also common in the
phylum
In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...
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 Kleiner Wasserbä ...
*tetraploid (four sets; 4''x''), for example,
Plains viscacha rat
The plains viscacha rat, plains vizcacha rat, red viscacha rat, or red vizcacha rat (''Tympanoctomys barrerae'') is a species of rodent in the family Octodontidae native to Argentina. It is one of three species in the genus '' Tympanoctomys''.
D ...
,
Salmonidae
Salmonidae is a family of ray-finned fish that constitutes the only currently extant family in the order Salmoniformes . It includes salmon (both Atlantic and Pacific species), trout (both ocean-going and landlocked), chars, freshwater whitefis ...
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, the wo ...
''
*pentaploid (five sets; 5''x''), for example Kenai Birch (''
Betula kenaica
''Betula kenaica'', or Kenai birch, is a species of birch that can be found in Alaska and northwestern North America at above sea level.
Description
It grows up to tall, with reddish-brown bark that may become pink or grayish-white. The leaf b ...
'')
*hexaploid (six sets; 6''x''), for example some species of
wheat
Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...
,
kiwifruit
Kiwifruit (often shortened to kiwi in North American, British and continental European English) or Chinese gooseberry is the edible berry of several species of woody vines in the genus '' Actinidia''. The most common cultivar group of kiwi ...
*heptaploid or septaploid (seven sets; 7''x'')
*octaploid or octoploid, (eight sets; 8''x''), for example ''
Acipenser
''Acipenser'' is a genus of sturgeons. With 17 living species (others are only known from fossil remains), it is the largest genus in the order Acipenseriformes. The genus is paraphyletic, containing all sturgeons that do not belong to ''Huso' ...
'' (genus of
sturgeon fish),
dahlia
Dahlia (, ) is a genus of bushy, tuberous, herbaceous perennial plants native to Mexico and Central America. A member of the Asteraceae (former name: Compositae) family of dicotyledonous plants, its garden relatives thus include the sunflower, ...
s
*decaploid (ten sets; 10''x''), for example certain
strawberries
The garden strawberry (or simply strawberry; ''Fragaria × ananassa'') is a widely grown hybrid species of the genus '' Fragaria'', collectively known as the strawberries, which are cultivated worldwide for their fruit. The fruit is widely ap ...
*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 herbaceous plant of tropical origin in the Amaranthaceae family from India and Nepal. The plant is known for its very bright colors. In India and China it is ...
'' and ''
Spartina anglica
''Sporobolus anglicus'' (common cordgrass) is a species of cordgrass that originated in southern England in about 1870 and is a neonative species in Britain. It was reclassified as '' Sporobolus anglicus'' after a taxonomic revision in 2014,Pe ...
'' or the amphibian ''
Xenopus ruwenzoriensis
The Uganda clawed frog (''Xenopus ruwenzoriensis'') is a species of frog in the family Pipidae found in Uganda and possibly the Democratic Republic of the Congo. Its natural habitats are subtropical or tropical moist lowland forest, freshwater ma ...
''.
Classification
Autopolyploidy
Autopolyploids are polyploids with multiple chromosome sets derived from a single
taxon
In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...
.
Two examples of natural autopolyploids are the piggyback plant, ''
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
Triploid block is a phenomenon describing the formation of nonviable progeny after hybridization of flowering plants that differ in ploidy. The barrier is established in the endosperm, a nutritive tissue supporting embryo growth. This phenomen ...
), 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 that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the fu ...
. In fact, stable autotriploidy in plants is often associated with
apomictic mating systems. In agricultural systems, autotriploidy can result in seedlessness, as in
watermelon
Watermelon (''Citrullus lanatus'') is a flowering plant species of the Cucurbitaceae family and the name of its edible fruit. A scrambling and trailing vine-like plant, it is a highly cultivated fruit worldwide, with more than 1,000 varieti ...
s and
bananas. 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 or treatment with
colchicine
Colchicine is a medication used to treat gout and Behçet's disease. In gout, it is less preferred to NSAIDs or steroids. Other uses for colchicine include the management of pericarditis and familial Mediterranean fever. Colchicine is taken b ...
,
oryzalin
Oryzalin is an herbicide of the dinitroaniline class. It acts through the disruption ( depolymerization) of microtubules, thus blocking anisotropic growth of plant cells. It can also be used to induce polyploid
Polyploidy is a condition in w ...
or
mitotic inhibitor
A mitotic inhibitor is a drug that inhibits mitosis, or cell division. These drugs disrupt microtubules, which are structures that pull the chromosomes apart when a cell divides. Mitotic inhibitors are used in cancer treatment, because cancer cell ...
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 by mitosis gives rise to genetically identical cells in which the total number of chromosomes is maintai ...
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 that pair up with each other inside a cell during fertilization. Homologs have the same genes in the same loci where they provide points alon ...
sets, which can lead to high rates of multivalent pairing during
meiosis
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...
(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 chromosomes in a cell, for example a human cell having 45 or 47 chromosomes instead of the usual 46. It does not include a difference of one or more complete sets of chromosomes. A cell with any ...
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
Homology may refer to:
Sciences
Biology
*Homology (biology), any characteristic of biological organisms that is derived from a common ancestor
* Sequence homology, biological homology between DNA, RNA, or protein sequences
*Homologous chrom ...
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 taxon – or reduced gametes from two autotetraploid taxa – combine to form allopolyploid offspring. In the latter case, one or more diploid
F1 hybrids produce unreduced gametes that fuse to form allopolyploid progeny.
Hybridization followed by genome duplication may be a more common path to allopolyploidy because F
1 hybrids between taxa often have relatively high rates of unreduced gamete formation – divergence between the genomes of the two taxa result in abnormal pairing between
homoeologous chromosomes or
nondisjunction
Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division (mitosis/meiosis). There are three forms of nondisjunction: failure of a pair of homologous chromosomes to separate in meiosis ...
during meiosis.
In this case, allopolyploidy can actually restore normal,
bivalent Bivalent 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 log ...
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, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism.
Mo ...
of homoeologous alleles. In certain cases, such heterozygosity can have beneficial
heterotic effects, either in terms of fitness in natural contexts or desirable traits in agricultural contexts. This could partially explain the prevalence of allopolyploidy among crop species. Both bread
wheat
Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...
and ''
Triticale
Triticale (; × ''Triticosecale'') is a hybrid of wheat (''Triticum'') and rye (''Secale'') first bred in laboratories during the late 19th century in Scotland and Germany. Commercially available triticale is almost always a second-generation ...
'' are examples of an allopolyploids with six chromosome sets.
Cotton
Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus ''Gossypium'' in the mallow family Malvaceae. The fiber is almost pure cellulose, and can contain minor perce ...
,
peanut
The peanut (''Arachis hypogaea''), also known as the groundnut, goober (US), pindar (US) or monkey nut (UK), is a legume crop grown mainly for its edible Seed, seeds. It is widely grown in the tropics and subtropics, important to both small ...
, or
quinoa
Quinoa (''Chenopodium quinoa''; , from Quechua ' or ') is a flowering plant in the amaranth family. It is a herbaceous annual plant grown as a crop primarily for its edible seeds; the seeds are rich in protein, dietary fiber, B vitamins, a ...
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 the six most commonly known members of the plant genus ''Brassica''. The theory states that the genomes of three ancestral diploid species of ''Brassica'' combined to ...
describes the relationships between the three common diploid Brassicas (''
B. oleracea,
B. rapa,'' and ''
B. nigra'') and three allotetraploids (''
B. napus,
B. juncea,'' and ''
B. carinata'') derived from hybridization among the diploid species. A similar relationship exists between three diploid species of ''
Tragopogon
''Tragopogon'', also known as goatsbeard or salsify, is a genus of flowering plants in the family Asteraceae. It includes the vegetable known as salsify, as well as a number of common wild flowers.
Salsifies are forbs growing as biennial or per ...
'' (''
T. dubius,
T. pratensis,'' and ''
T. porrifolius'') and two allotetraploid species (''
T. mirus'' and ''
T. miscellus''). Complex patterns of allopolyploid evolution have also been observed in animals, as in the frog genus ''
Xenopus
''Xenopus'' () (Gk., ξενος, ''xenos''=strange, πους, ''pous''=foot, commonly known as the clawed frog) is a genus of highly aquatic frogs native to sub-Saharan Africa. Twenty species are currently described within it. The two best-know ...
.''
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 chromosomes in a cell, for example a human cell having 45 or 47 chromosomes instead of the usual 46. It does not include a difference of one or more complete sets of chromosomes. A cell with any ...
(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
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...
tissues.
This is known as endopolyploidy. Species whose cells do not have nuclei, that is,
prokaryotes
A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Connec ...
, may be polyploid, as seen in the large
bacterium
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
''
Epulopiscium fishelsoni
"''Candidatus'' Epulonipiscium" is a genus of Gram-positive bacteria that have a symbiotic relationship with surgeonfish. These bacteria are known for their unusually large size, many ranging from 200–700 μm in length. Until the discovery of ...
''. 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.
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
![PaleopolyploidyTree](https://upload.wikimedia.org/wikipedia/commons/3/35/PaleopolyploidyTree.jpg)
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
Diploidization is the process of converting a polyploid genome back into a diploid one. Polyploidy is a product of whole genome duplication (WGD) and is followed by diploidization as a result of genome shock. The plant kingdom has undergone multi ...
(such that a polyploid starts to behave cytogenetically as a diploid over time) as
mutation
In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mi ...
s 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
sequenced genomes. Examples of unexpected but recently confirmed ancient genome duplications include
baker's yeast
Baker's yeast is the common name for the strains of yeast commonly used in baking bread and other bakery products, serving as a leavening agent which causes the bread to rise (expand and become lighter and softer) by converting the fermentabl ...
(''
Saccharomyces cerevisiae
''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungus microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have been o ...
''), mustard weed/thale cress (''
Arabidopsis thaliana
''Arabidopsis thaliana'', the thale cress, mouse-ear cress or arabidopsis, is a small flowering plant native to Eurasia and Africa. ''A. thaliana'' is considered a weed; it is found along the shoulders of roads and in disturbed land.
A winter a ...
''),
rice
Rice is the seed of the grass species ''Oryza sativa'' (Asian rice) or less commonly ''Oryza glaberrima
''Oryza glaberrima'', commonly known as African rice, is one of the two domesticated rice species. It was first domesticated and grown i ...
(''
Oryza sativa
''Oryza sativa'', commonly known as Asian rice or indica rice, is the plant species most commonly referred to in English as ''rice''. It is the type of farmed rice whose cultivars are most common globally, and was first domesticated in the Yan ...
''), and an early
evolution
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
ary
ancestor
An ancestor, also known as a forefather, fore-elder or a forebear, is a parent or (recursively) the parent of an antecedent (i.e., a grandparent, great-grandparent, great-great-grandparent and so forth). ''Ancestor'' is "any person from whom ...
of the
vertebrates
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
(which includes the
human
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...
lineage) and another near the origin of the
teleost
Teleostei (; Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts ), is, by far, the largest infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of all extant species of fish. Tele ...
fishes
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
.
Angiosperm
Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...
s (
flowering plant
Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...
s) 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 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 individuals of the appropriate s ...
. The preparation and study of karyotypes is part of
cytology
Cell biology (also cellular biology or cytology) is a branch of biology that studies the structure, function, and behavior of cells. All living organisms are made of cells. A cell is the basic unit of life that is responsible for the living an ...
and, more specifically,
cytogenetics
Cytogenetics is essentially a branch of genetics, but is also a part of cell biology/cytology (a subdivision of human anatomy), that is concerned with how the chromosomes relate to cell behaviour, particularly to their behaviour during mitosis an ...
.
Although the replication and transcription of DNA is highly standardized in
eukaryotes, the same cannot be said for their karyotypes, which are highly variable between species in chromosome number and in detailed organization despite being constructed out of the same macromolecules. In some cases, there is even significant variation within species. This variation provides the basis for a range of studies in what might be called evolutionary cytology.
Homoeologous chromosomes
Homoeologous chromosomes are those brought together following
inter-species hybridization and
allopolyploidization, and whose relationship was completely homologous in an ancestral species. For example,
durum wheat
Durum wheat (), also called pasta wheat or macaroni wheat (''Triticum durum'' or ''Triticum turgidum'' subsp. ''durum''), is a tetraploid species of wheat. It is the second most cultivated species of wheat after common wheat, although it represe ...
is the result of the inter-species hybridization of two diploid grass species ''Triticum urartu'' and ''Aegilops speltoides''. Both diploid ancestors had two sets of 7 chromosomes, which were similar in terms of size and genes contained on them. Durum wheat contains a
hybrid genome with two sets of chromosomes derived from ''Triticum urartu'' and two sets of chromosomes derived from ''Aegilops speltoides''. Each chromosome pair derived from the ''Triticum urartu'' parent is homoeologous to the opposite chromosome pair derived from the ''Aegilops speltoides'' parent, though each chromosome pair unto itself is homologous.
Examples
Animals
Examples in animals are more common in non-vertebrates such as
flatworm
The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") are a phylum of relatively simple bilaterian, unsegment ...
s,
leeches, and
brine shrimp
''Artemia'' is a genus of aquatic crustaceans also known as brine shrimp. It is the only genus in the family Artemiidae. The first historical record of the existence of ''Artemia'' dates back to the first half of the 10th century AD from Urmia L ...
. Within vertebrates, examples of stable polyploidy include the
salmonids
Salmonidae is a family of ray-finned fish that constitutes the only currently extant family in the order Salmoniformes . It includes salmon (both Atlantic and Pacific species), trout (both ocean-going and landlocked), chars, freshwater whit ...
and many
cyprinids
Cyprinidae is a family of freshwater fish commonly called the carp or minnow family. It includes the carps, the true minnows, and relatives like the barbs and barbels. Cyprinidae is the largest and most diverse fish family and the largest vert ...
(i.e.
carp
Carp are various species of oily freshwater fish from the family Cyprinidae, a very large group of fish native to Europe and Asia. While carp is consumed in many parts of the world, they are generally considered an invasive species in parts of ...
).
Some fish have as many as 400 chromosomes.
Polyploidy also occurs commonly in amphibians; for example the biomedically important genus ''
Xenopus
''Xenopus'' () (Gk., ξενος, ''xenos''=strange, πους, ''pous''=foot, commonly known as the clawed frog) is a genus of highly aquatic frogs native to sub-Saharan Africa. Twenty species are currently described within it. The two best-know ...
'' 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
Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and development ...
; others, like ''
Liolaemus chiliensis
''Liolaemus chiliensis'' (Chilean tree iguana) is a species of lizard in the family Liolaemidae, also referred to as the weeping or crying lizard in English. Synonyms for this species include "Liodeira chilensis" and Calotes chiliensis."THE REPT ...
'', maintain sexual reproduction. Polyploid
mole salamanders
The mole salamanders (genus ''Ambystoma'') are a group of advanced salamanders endemic to North America. The group has become famous due to the presence of the axolotl (''A. mexicanum''), widely used in research due to its paedomorphosis, and ...
(mostly triploids) are all female and reproduce by
kleptogenesis
In biology, a klepton (abbr. kl.) and synklepton (abbr sk.) is a species that requires input from another biological taxon (normally from a species which is closely related to the kleptonic species) to complete its reproductive cycle. Specific typ ...
,
"stealing"
spermatophore
A spermatophore or sperm ampulla is a capsule or mass containing spermatozoa created by males of various animal species, especially salamanders and arthropods, and transferred in entirety to the female's ovipore during reproduction. Spermatophores ...
s 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
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
are known, but most often result in
prenatal
Prenatal development () includes the development of the embryo and of the fetus during a viviparous animal's gestation. Prenatal development starts with fertilization, in the germinal stage of embryonic development, and continues in fetal devel ...
death. An
octodontid
Octodontidae is a family of rodents, restricted to southwestern South America. Fourteen species of octodontid are recognised, arranged in seven genera. The best known species is the common degu, ''Octodon degus''.
Octodontids are medium-sized ...
rodent
Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are na ...
of
Argentina
Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
's harsh
desert
A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About on ...
regions, known as the
plains viscacha rat
The plains viscacha rat, plains vizcacha rat, red viscacha rat, or red vizcacha rat (''Tympanoctomys barrerae'') is a species of rodent in the family Octodontidae native to Argentina. It is one of three species in the genus '' Tympanoctomys''.
D ...
(''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 pig
The guinea pig or domestic guinea pig (''Cavia porcellus''), also known as the cavy or domestic cavy (), is a species of rodent belonging to the genus ''Cavia'' in the family Caviidae. Breeders tend to use the word ''cavy'' to describe the ani ...
s 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
Andean
The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S l ...
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
Har Swarup, FNA (9 December 1922 – 25 April 1981) was vice-chancellor, academician, and scientist in the field of developmental biology and genetic engineering as well as an academician and teacher of molecular biology and biochemistry. He i ...
(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
Sir John Bertrand Gurdon (born 2 October 1933) is a British developmental biologist. He is best known for his pioneering research in nuclear transplantation and cloning. He was awarded the Lasker Award in 2009. In 2012, he and Shinya Yamanaka ...
(1958) transplanted intact nuclei from somatic cells to produce diploid eggs in the frog, ''
Xenopus
''Xenopus'' () (Gk., ξενος, ''xenos''=strange, πους, ''pous''=foot, commonly known as the clawed frog) is a genus of highly aquatic frogs native to sub-Saharan Africa. Twenty species are currently described within it. The two best-know ...
'' (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
John Burdon Sanderson Haldane (; 5 November 18921 December 1964), nicknamed "Jack" or "JBS", was a British-Indian scientist who worked in physiology, genetics, evolutionary biology, and mathematics. With innovative use of statistics in biolog ...
hailed the work for its potential medical applications and, in describing the results, became one of the first to use the word "
clone" in reference to animals. Later work by
Shinya Yamanaka
is a Japanese stem cell researcher and a Nobel Prize laureate. He serves as the director of Center for iPS Cell (induced Pluripotent Stem Cell) Research and Application and a professor at the Institute for Frontier Medical Sciences at Kyo ...
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
differentiated tissue, such as liver
parenchyma, heart muscle, placenta and in bone marrow.
Aneuploidy
Aneuploidy is the presence of an abnormal number of chromosomes in a cell, for example a human cell having 45 or 47 chromosomes instead of the usual 46. It does not include a difference of one or more complete sets of chromosomes. A cell with any ...
is more common.
Polyploidy occurs in humans in the form of
triploidy
Polyploidy is a condition in which the cells of an organism have more than one pair of ( homologous) chromosomes. Most species whose cells have nuclei ( eukaryotes) are diploid, meaning they have two sets of chromosomes, where each set contain ...
, with 69 chromosomes (sometimes called 69, XXX), and tetraploidy with 92 chromosomes (sometimes called 92, XXXX). Triploidy, usually due to
polyspermy
In biology, polyspermy describes the fertilization of an egg by more than one sperm. Diploid organisms normally contain two copies of each chromosome, one from each parent. The cell resulting from polyspermy, on the other hand, contains three or ...
, occurs in about 2–3% of all human pregnancies and ~15% of miscarriages. The vast majority of triploid conceptions end as a
miscarriage
Miscarriage, also known in medical terms as a spontaneous abortion and pregnancy loss, is the death of an embryo or fetus before it is able to survive independently. Miscarriage before 6 weeks of gestation is defined by ESHRE as biochemical lo ...
; those that do survive to term typically die shortly after birth. In some cases, survival past birth may be extended if there is
mixoploidy
Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...
with both a
diploid and a triploid cell population present. There has been one report of a child surviving to the age of seven months with complete triploidy syndrome. He failed to exhibit normal mental or physical neonatal development, and died from a ''
Pneumocystis carinii
''Pneumocystis jirovecii'' (previously ''P. carinii'') is a yeast-like fungus of the genus ''Pneumocystis''. The causative organism of ''Pneumocystis'' pneumonia, it is an important human pathogen, particularly among immunocompromised hosts. P ...
'' infection, which indicates a weak immune system.
Triploidy may be the result of either
digyny
Digyny (also digynia) refers to the process of a diploid ovum becoming fertilized by a monoploid sperm. The result of digyny is a triploid zygote. In humans, both gametes (ovum and sperm) are normally monoploid and give rise to a diploid zygote.
...
(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
Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...
of the egg.
Digyny is most commonly caused by either failure of one meiotic division during oogenesis leading to a diploid
oocyte
An oocyte (, ), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female ...
or failure to extrude one
polar body
A polar body is a small haploid cell that is formed at the same time as an egg cell during oogenesis, but generally does not have the ability to be fertilized. It is named from its polar position in the egg.
When certain diploid cells in animals ...
from the
oocyte
An oocyte (, ), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female ...
. Diandry appears to predominate among early
miscarriage
Miscarriage, also known in medical terms as a spontaneous abortion and pregnancy loss, is the death of an embryo or fetus before it is able to survive independently. Miscarriage before 6 weeks of gestation is defined by ESHRE as biochemical lo ...
s, 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
phenotype
In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological proper ...
s in triploid
placenta
The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mater ...
s and
fetus
A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal deve ...
es that are dependent on the origin of the extra
haploid set. In digyny, there is typically an asymmetric poorly grown
fetus
A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal deve ...
, with marked
adrenal
The adrenal glands (also known as suprarenal glands) are endocrine glands that produce a variety of hormones including adrenaline and the steroids aldosterone and cortisol. They are found above the kidneys. Each gland has an outer cortex whic ...
hypoplasia and a very small
placenta
The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mater ...
. In diandry, a partial
hydatidiform mole develops.
These parent-of-origin effects reflect the effects of
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
Prenatal testing consists of prenatal screening and prenatal diagnosis, which are aspects of prenatal care that focus on detecting problems with the pregnancy as early as possible. These may be anatomic and physiologic problems with the health of ...
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
Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...
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.
Fish
A polyploidy event occurred within the stem lineage of the teleost fish.
Plants
![Polyploidization](https://upload.wikimedia.org/wikipedia/commons/0/04/Polyploidization.svg)
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
Paleopolyploidy is the result of genome duplications which occurred at least several million years ago (MYA). Such an event could either double the genome of a single species ( autopolyploidy) or combine those of two species (allopolyploidy). B ...
) in their genomes.
Huge explosions in
angiosperm
Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...
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
Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within ...
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
Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within ...
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 crosses, such as between polyploids and their parent species, usually have aberrant endosperm development which impairs their viability, thus contributing to
polyploid speciation
Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within ...
.
Some plants are triploid. As
meiosis
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...
is disturbed, these plants are sterile, with all plants having the same genetic constitution: Among them, the exclusively vegetatively propagated
saffron crocus
''Crocus sativus'', commonly known as saffron crocus or autumn crocus, is a species of flowering plant in the iris family (biology), family Iridaceae. A cormous autumn-flowering cultivated perennial plant, perennial, unknown in the wild, it is ...
(''Crocus sativus''). Also, the extremely rare Tasmanian shrub ''
Lomatia tasmanica
''Lomatia tasmanica'', commonly known as King's lomatia, is a shrub of the family Proteaceae native to Tasmania. Growing up to tall, the plant has shiny green pinnate (lobed) leaves and bears red flowers in the summer, but yields neither fru ...
'' is a triploid sterile species.
There are few naturally occurring polyploid
conifers. One example is the Coast Redwood ''
Sequoia sempervirens
''Sequoia sempervirens'' ()''Sunset Western Garden Book,'' 1995:606–607 is the sole living species of the genus '' Sequoia'' in the cypress family Cupressaceae (formerly treated in Taxodiaceae). Common names include coast redwood, coastal ...
'', which is a hexaploid (6''x'') with 66 chromosomes (2''n'' = 6''x'' = 66), although the origin is unclear.
Aquatic plants, especially the
Monocotyledon
Monocotyledons (), commonly referred to as monocots, (Lilianae ''sensu'' Chase & Reveal) are grass and grass-like flowering plants (angiosperms), the seeds of which typically contain only one embryonic leaf, or cotyledon. They constitute one of ...
s, 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
Triticale (; × ''Triticosecale'') is a hybrid of wheat (''Triticum'') and rye (''Secale'') first bred in laboratories during the late 19th century in Scotland and Germany. Commercially available triticale is almost always a second-generation ...
is the hybrid of
wheat
Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...
(''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
Grafting or graftage is a horticultural technique whereby tissues of plants are joined so as to continue their growth together. The upper part of the combined plant is called the scion () while the lower part is called the rootstock. The succ ...
.
Polyploidy in crop plants is most commonly induced by treating seeds with the chemical
colchicine
Colchicine is a medication used to treat gout and Behçet's disease. In gout, it is less preferred to NSAIDs or steroids. Other uses for colchicine include the management of pericarditis and familial Mediterranean fever. Colchicine is taken b ...
.
= Examples
=
* Triploid crops: some
apple
An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple fruit tree, trees are agriculture, cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, wh ...
varieties (such as
Belle de Boskoop
Belle de Boskoop (also called Goudrenet, Goudreinet or Goudreinnette) is an apple cultivar which originated in Boskoop, Netherlands, where it began as a chance seedling in 1856. Variants include Boskoop red, yellow and green. This rustic apple is ...
,
Jonagold,
Mutsu,
Ribston Pippin
'Ribston Pippin' is a triploid cultivar of apples, also known by other names including 'Essex Pippin', 'Beautiful Pippin', 'Formosa', 'Glory of York', 'Ribstone', 'Rockhill's Russet', 'Travers', and 'Travers's Reinette'.
Origin
This apple was gro ...
),
banana,
citrus
''Citrus'' is a genus of flowering plant, flowering trees and shrubs in the rue family, Rutaceae. Plants in the genus produce citrus fruits, including important crops such as Orange (fruit), oranges, Lemon, lemons, grapefruits, pomelos, and lim ...
,
ginger
Ginger (''Zingiber officinale'') is a flowering plant whose rhizome, ginger root or ginger, is widely used as a spice
A spice is a seed, fruit, root, bark, or other plant substance primarily used for flavoring or coloring food. Spices ...
,
watermelon
Watermelon (''Citrullus lanatus'') is a flowering plant species of the Cucurbitaceae family and the name of its edible fruit. A scrambling and trailing vine-like plant, it is a highly cultivated fruit worldwide, with more than 1,000 varieti ...
,
saffron crocus
''Crocus sativus'', commonly known as saffron crocus or autumn crocus, is a species of flowering plant in the iris family (biology), family Iridaceae. A cormous autumn-flowering cultivated perennial plant, perennial, unknown in the wild, it is ...
, white pulp of coconut
* Tetraploid crops: very few
apple
An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple fruit tree, trees are agriculture, cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, wh ...
varieties,
durum
Durum wheat (), also called pasta wheat or macaroni wheat (''Triticum durum'' or ''Triticum turgidum'' subsp. ''durum''), is a tetraploid species of wheat. It is the second most cultivated species of wheat after common wheat, although it represen ...
or
macaroni wheat
Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...
,
cotton
Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus ''Gossypium'' in the mallow family Malvaceae. The fiber is almost pure cellulose, and can contain minor perce ...
,
potato
The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae.
Wild potato species can be found from the southern Unit ...
,
canola
Close-up of canola blooms
Canola flower
Rapeseed oil is one of the oldest known vegetable oils. There are both edible and industrial forms produced from rapeseed, the seed of several cultivars of the plant family Brassicaceae. Historically, ...
/
rapeseed
Rapeseed (''Brassica napus ''subsp.'' napus''), also known as rape, or oilseed rape, is a bright-yellow flowering member of the family Brassicaceae (mustard or cabbage family), cultivated mainly for its oil-rich seed, which naturally contains a ...
,
leek,
tobacco
Tobacco is the common name of several plants in the genus '' Nicotiana'' of the family Solanaceae, and the general term for any product prepared from the cured leaves of these plants. More than 70 species of tobacco are known, but the ...
,
peanut
The peanut (''Arachis hypogaea''), also known as the groundnut, goober (US), pindar (US) or monkey nut (UK), is a legume crop grown mainly for its edible Seed, seeds. It is widely grown in the tropics and subtropics, important to both small ...
,
kinnow
The Kinnow is a high yield mandarin hybrid cultivated extensively in the wider Punjab region of India and Pakistan.
It is a hybrid of two citrus cultivars — 'King' (''Citrus nobilis'') × 'Willow Leaf' (''Citrus × deliciosa'') — first dev ...
,
Pelargonium
* Hexaploid crops:
chrysanthemum, bread
wheat
Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...
,
triticale
Triticale (; × ''Triticosecale'') is a hybrid of wheat (''Triticum'') and rye (''Secale'') first bred in laboratories during the late 19th century in Scotland and Germany. Commercially available triticale is almost always a second-generation ...
,
oat
The oat (''Avena sativa''), sometimes called the common oat, is a species of cereal grain grown for its seed, which is known by the same name (usually in the plural, unlike other cereals and pseudocereals). While oats are suitable for human con ...
,
kiwifruit
Kiwifruit (often shortened to kiwi in North American, British and continental European English) or Chinese gooseberry is the edible berry of several species of woody vines in the genus '' Actinidia''. The most common cultivar group of kiwi ...
* Octaploid crops:
strawberry
The garden strawberry (or simply strawberry; ''Fragaria × ananassa'') is a widely grown hybrid species of the genus '' Fragaria'', collectively known as the strawberries, which are cultivated worldwide for their fruit. The fruit is widely ap ...
,
dahlia
Dahlia (, ) is a genus of bushy, tuberous, herbaceous perennial plants native to Mexico and Central America. A member of the Asteraceae (former name: Compositae) family of dicotyledonous plants, its garden relatives thus include the sunflower, ...
,
pansies
The garden pansy (''Viola'' × ''wittrockiana'') is a type of large-flowered hybrid plant cultivated as a garden flower. It is derived by hybridization from several species in the section ''Melanium'' ("the pansies") of the genus ''Viola'', p ...
,
sugar cane
Sugarcane or sugar cane is a species of (often hybrid) tall, perennial grass (in the genus ''Saccharum'', tribe Andropogoneae) that is used for sugar production. The plants are 2–6 m (6–20 ft) tall with stout, jointed, fibrous stalks t ...
, oca (''
Oxalis tuberosa
''Oxalis tuberosa'' is a perennial herbaceous plant that overwinters as underground stem tubers. These tubers are known as uqa in Quechua, oca in Spanish, yam in New Zealand and a number of other alternative names. The plant was brought into cult ...
'')
* Dodecaploid crops: some
sugar cane
Sugarcane or sugar cane is a species of (often hybrid) tall, perennial grass (in the genus ''Saccharum'', tribe Andropogoneae) that is used for sugar production. The plants are 2–6 m (6–20 ft) tall with stout, jointed, fibrous stalks t ...
hybrids
Some crops are found in a variety of ploidies:
tulip
Tulips (''Tulipa'') are a genus of spring-blooming perennial herbaceous bulbiferous geophytes (having bulbs as storage organs). The flowers are usually large, showy and brightly coloured, generally red, pink, yellow, or white (usually in warm ...
s and
lilies
''Lilium'' () is a genus of herbaceous flowering plants growing from bulbs, all with large prominent flowers. They are the true lilies. Lilies are a group of flowering plants which are important in culture and literature in much of the world. M ...
are commonly found as both diploid and triploid;
daylilies
A daylily or day lily is a flowering plant in the genus ''Hemerocallis'' , a member of the family Asphodelaceae, subfamily Hemerocallidoideae. Despite the common name, it is not in fact a lily. Gardening enthusiasts and horticulturists have long ...
(''Hemerocallis'' cultivars) are available as either diploid or tetraploid; apples and
kinnow mandarins can be diploid, triploid, or tetraploid.
Fungi
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
for review). Several examples of polyploids are known:
*autopolyploid: the aquatic fungi of genus ''Allomyces'', some ''
Saccharomyces cerevisiae
''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungus microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have been o ...
'' strains used in
bakery, etc.
*allopolyploid: the widespread ''
Cyathus stercoreus
''Cyathus stercoreus'', commonly known as the dung-loving bird's nest or the dung bird's nest, is a species of fungus in the genus '' Cyathus'', family Nidulariaceae. Like other species in the Nidulariaceae, the fruiting bodies of ''C. sterc ...
'', the allotetraploid lager yeast ''
Saccharomyces pastorianus
''Saccharomyces pastorianus'' is a yeast used industrially for the production of lager beer, and was named in honour of Louis Pasteur by the German Max Reess in 1870. This yeast's complicated genome appears to be the result of hybridisation bet ...
'', the allotriploid wine spoilage yeast ''
Dekkera bruxellensis
''Brettanomyces bruxellensis'' (the anamorph of ''Dekkera bruxellensis'') is a yeast associated with the Senne valley near Brussels, Belgium. Despite its Latin species name, ''B. bruxellensis'' is found all over the globe. In the wild, it is oft ...
'', etc.
*paleopolyploid: the human pathogen ''
Rhizopus oryzae
''Rhizopus oryzae'' is a filamentous heterothallic microfungus that occurs as a saprotroph in soil, dung, and rotting vegetation. This species is very similar to ''Rhizopus stolonifer'', but it can be distinguished by its smaller sporangia and a ...
'', the genus ''
Saccharomyces
''Saccharomyces'' is a genus of fungi that includes many species of yeasts. ''Saccharomyces'' is from Greek σάκχαρον (sugar) and μύκης (fungus) and means ''sugar fungus''. Many members of this genus are considered very important in f ...
'', etc.
In addition, polyploidy is frequently associated with
hybridization and reticulate evolution that appear to be highly prevalent in several fungal taxa. Indeed,
homoploid speciation (hybrid speciation without a change in
chromosome
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
number) has been evidenced for some fungal species (such as the
basidiomycota
Basidiomycota () is one of two large divisions that, together with the Ascomycota, constitute the subkingdom Dikarya (often referred to as the "higher fungi") within the kingdom Fungi. Members are known as basidiomycetes. More specifically, Basi ...
''
Microbotryum violaceum'').
![Polyploidy in fungi](https://upload.wikimedia.org/wikipedia/commons/0/07/Polyploidy_in_fungi.png)
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
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
The transcriptome is the set of all RNA transcripts, including coding and non-coding, in an individual or a population of cells. The term can also sometimes be used to refer to all RNAs, or just mRNA, depending on the particular experiment. The t ...
.
Phenotypic
In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological proper ...
diversification is also observed following polyploidization and/or hybridization in fungi, producing the fuel for
natural selection
Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charle ...
and subsequent
adaptation
In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...
and speciation.
Chromalveolata
Other eukaryotic
taxa
In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...
have experienced one or more polyploidization events during their evolutionary history (see Albertin and Marullo, 2012
for review). The
oomycetes
Oomycota forms a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms, called oomycetes (). They are filamentous and heterotrophic, and can reproduce both sexually and asexually. Sexual reproduction of an oospore is the result ...
, which are non-true fungi members, contain several examples of paleopolyploid and polyploid species, such as within the genus ''
Phytophthora
''Phytophthora'' (from Greek (''phytón''), "plant" and (), "destruction"; "the plant-destroyer") is a genus of plant-damaging oomycetes (water molds), whose member species are capable of causing enormous economic losses on crops worldwide, a ...
''. Some species of brown
algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
(
Fucales
The Fucales (fucoids) are an order in the brown algae (class Phaeophyceae). The list of families in the Fucales, as well as additional taxonomic information on algae, is publicly accessible at Algaebaseref name="Guiry and Guiry">Guiry, M.D. and ...
, Laminariales and
diatoms
A diatom (New Latin, Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group com ...
) contain apparent polyploid genomes. In the
Alveolata group, the remarkable species ''
Paramecium
''
''Paramecium'' ( , ; also spelled ''Paramoecium'') is a genus of eukaryotic, unicellular ciliates, commonly studied as a representative of the ciliate group. ''Paramecia'' are widespread in freshwater, brackish, and marine environments and a ...
tetraurelia'' underwent three successive rounds of whole-genome duplication
and established itself as a major model for paleopolyploid studies.
Bacteria
Each ''
Deinococcus radiodurans
''Deinococcus radiodurans'' is an extremophilic bacterium and one of the most radiation-resistant organisms known. It can survive cold, dehydration, vacuum, and acid, and therefore is known as a polyextremophile. It has been listed as the world ...
''
bacterium
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
contains 4-8 copies of its
chromosome
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
.
Exposure of ''D. radiodurans'' to
X-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...
irradiation or
desiccation
Desiccation () is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic (attracts and holds water) substance that induces or sustains such a state in its local vicinity in a moderately sealed container.
...
can shatter its
genome
In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...
s 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
Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in cellular organisms but may ...
and a process referred to as extended
synthesis-dependent strand annealing (SDSA).
''
Azotobacter vinelandii
''Azotobacter vinelandii'' is Gram-negative diazotroph that can fix nitrogen while grown aerobically. These bacteria are easily cultured and grown.
''A. vinelandii'' is a free-living N2 fixer known to produce many phytohormones and vitamins in ...
'' 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
archaeon
Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebact ...
''
Halobacterium salinarium'' is polyploid
and, like ''
Deinococcus radiodurans
''Deinococcus radiodurans'' is an extremophilic bacterium and one of the most radiation-resistant organisms known. It can survive cold, dehydration, vacuum, and acid, and therefore is known as a polyextremophile. It has been listed as the world ...
'', 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
DNA-binding proteins are proteins that have DNA-binding domains and thus have a specific or general affinity for single- or double-stranded DNA. Sequence-specific DNA-binding proteins generally interact with the major groove of B-DNA, becaus ...
and is likely
homologous recombination
Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in cellular organisms but may ...
al repair.
See also
*
Diploidization
Diploidization is the process of converting a polyploid genome back into a diploid one. Polyploidy is a product of whole genome duplication (WGD) and is followed by diploidization as a result of genome shock. The plant kingdom has undergone multi ...
*
Eukaryote hybrid genome
Eukaryote hybrid genomes result from interspecific hybridization, where closely related species mate and produce offspring with admixed genomes. The advent of large-scale genomic sequencing has shown that hybridization is common, and that it may ...
*
Ploidy
*
Polyploid complex
*
Polysomy
Polysomy is a condition found in many species, including fungi, plants, insects, and mammals, in which an organism has at least one more chromosome than normal, i.e., there may be three or more copies of the chromosome rather than the expected t ...
*
Reciprocal silencing
*
Sympatry
References
Further reading
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External links
Polyploidy on Kimball's Biology PagesThe polyploidy portala community-editable project with information, research, education, and a bibliography about polyploidy.
{{Authority control
Classical genetics
Speciation
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