Polyploidy
Encyclopedia
Polyploid is a term used to describe cells and organism
s containing more than two paired (homologous
) sets of chromosomes. Most eukaryotic
species are diploid, meaning they have two sets of chromosomes — one set inherited from each parent. However polyploidy is found in some organisms and is especially common in plants. In addition, polyploidy also occurs in some tissues of animals who are otherwise diploid, such as human muscle tissues. This is known as endopolyploidy. (Monoploid
organisms also occur; a monoploid has only one set of chromosomes. These include the vast majority of prokaryotes.)
Polyploidy refers to a numerical change in a whole set of chromosomes. Organisms in which a particular chromosome, or chromosome segment, is under- or overrepresented are said to be aneuploid
(from the Greek words meaning "not," "good," and "fold"). Therefore the distinction between aneuploidy and polyploidy is that aneuploidy refers to a numerical change in part of the chromosome set, whereas polyploidy refers to a numerical change in the whole set of chromosomes.
Polyploidy may occur due to abnormal cell division
, either during mitosis
, or commonly during metaphase I in meiosis
.
Polyploidy occurs in some animal
s, such as goldfish
, salmon
, and salamander
s, but is especially common among fern
s and flowering plant
s (see Hibiscus rosa-sinensis), including both wild and cultivated species
. Wheat
, for example, after millennia of hybridization and modification by humans, has strains that are diploid (two sets of chromosomes), tetraploid (four sets of chromosomes) with the common name of durum
or macaroni wheat, and hexaploid (six sets of chromosomes) with the common name of bread wheat. Many agriculturally important plants of the genus Brassica
are also tetraploids. Polyploidization is a mechanism of sympatric speciation
because polyploids are usually unable to interbreed with their diploid ancestors.
Polyploidy can be induced in plants and cell culture
s by some chemicals: the best known is colchicine
, which can result in chromosome doubling, though its use may have other less obvious consequences as well. Oryzalin
also will double the existing chromosome content.
:
s, leech
es, and brine shrimp
. Polyploid animals are often sterile, so they often reproduce by parthenogenesis
. Polyploid lizards are also quite common and parthenogenetic. Polyploid mole salamanders (mostly triploids) are all female and reproduce by kleptogenesis, "stealing" spermatophore
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 are known, but most often result in prenatal death.
An octodontid
rodent
of Argentina
's harsh desert
regions, known as the Plains Viscacha-Rat (Tympanoctomys barrerae) has been reported as an exception to this 'rule'. 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. The rodent is not a rat
, but kin to guinea pig
s and chinchilla
s. Its "new" diploid [2n] number is 102 and so its cells are roughly twice normal size. Its closest living relation is Octomys mimax, the Andean
Viscacha-Rat of the same family, whose 2n = 56. It was therefore surmised that an Octomys-like ancestor produced tetraploid (i.e., 4n = 112) offspring that were, by virtue of their doubled chromosomes, reproductively isolated from their parents.
is more common.
Polyploidy occurs in humans in the form of triploidy, with 69 chromosomes (sometimes called 69,XXX), and tetraploidy with 92 chromosomes (sometimes called 92,XXXX). Triploidy, usually due to polyspermy
, occurs in about 2–3% of all human pregnancies and ~15% of miscarriages. The vast majority of triploid conceptions end as miscarriage
and those that do survive to term typically die shortly after birth. In some cases survival past birth may occur longer if there is mixoploidy with both a diploid and a triploid cell population present.
Triploidy may be the result of either digyny (the extra haploid set is from the mother) or diandry (the extra haploid set is from the father). Diandry is mostly caused by reduplication of the paternal haploid set from a single sperm, but may also be the consequence of dispermic (two sperm) fertilization of the egg. 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 miscarriage
s while digyny predominates among triploidy that survives into the fetal period. However, among early miscarriages, digyny is also more common in those cases <8.5 weeks gestational age or those in which an embryo is present. There are also two distinct phenotype
s in triploid placenta
s and fetus
es that are dependent on the origin of the extra haploid set. In digyny there is typically an asymmetric poorly grown fetus
, with marked adrenal hypoplasia
and a very small placenta
. 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
and these are generally considered 'harmless'. It is not clear whether these tetraploid cells simply tend to arise during in vitro cell culture or whether they are also present in placental cells in vivo. There are, at any rate, very few clinical reports of fetuses/infants diagnosed with tetraploidy mosaicism.
Mixoploidy is quite commonly observed in human preimplantation embryos and includes haploid/diploid as well as diploid/tetraploid mixed cell populations. It is unknown whether these embryos fail to implant and are therefore rarely detected in ongoing pregnancies or if there is simply a selective process favoring the diploid cells.
Polyploidy is pervasive in plants and some estimates suggest that 30–80% of living plant species are polyploid, and many lineages show evidence of ancient polyploidy (paleopolyploidy
) in their genomes. 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 (2n) gametes. Both autopolyploids (e.g. potato) and allopolyploids (e.g. canola, wheat, cotton) can be found among both wild and domesticated plant species. Most polyploids display heterosis
relative to their parental species, and may display novel variation or morphologies that may contribute to the processes of speciation
and eco-niche exploitation. 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.
Lomatia tasmanica is an extremely rare Tasmanian shrub which is triploid and sterile, and reproduction is entirely vegetative with all plants having the same genetic structure.
There are few naturally occurring polyploid conifers. One example is the giant tree
Sequoia sempervirens or Coast Redwood which is a hexaploid (6x) with 66 chromosomes (2n = 6x = 66), although the origin is unclear.
is the hybrid of wheat (Triticum turgidum) and rye
(Secale cereale). It combines sought-after characteristics of the parents, but the initial hybrids are sterile. After polyploidization, the hybrid becomes fertile and can thus be further propagated to become triticale.
In some situations polyploid crops are preferred because they are sterile. For example many seedless fruit varieties are seedless as a result of polyploidy. Such crops are propagated using asexual techniques such as grafting.
Polyploidy in crop plants is most commonly induced by treating seeds with the chemical colchicine.
Some crops are found in a variety of ploidies: tulip
s and lilies are commonly found as both diploid and as triploid; daylilies (Hemerocallis cultivars) are available as either diploid or tetraploid; apples and kinnow
s can be diploid, triploid, or tetraploid.
doubling, like the potato. Others might form following fusion of 2n gametes (unreduced gametes). Bananas and apples can be found as autotriploids. Autopolyploid plants typically display polysomic inheritance, and are therefore often infertile and propagated clonally perfect.
is an example of an allopolyploid, having six chromosome sets, allohexaploid, four from wheat (Triticum turgidum) and two from rye (Secale cereale). Amphidiploid is another word for an allopolyploid. Some of the best examples of allopolyploids come from the Brassicas, and the Triangle of U
describes the relationships among the three common diploid Brassicas (B. oleracea, B. rapa, and B. nigra) and three allotetraploids (B. napus, B. juncea, and B. carinata) derived from hybridization among the diploids.
can be difficult to detect because of subsequent diploidization (such that a polyploid starts to behave cytogenetically as a diploid over time) as mutation
s and gene translations gradually make one copy of each chromosome unlike its other copy.
In many cases, these events can be inferred only through comparing sequenced genomes
. Examples of unexpected but recently confirmed ancient genome duplications include baker's yeast
(Saccharomyces cerevisiae
), mustard weed/thale cress (Arabidopsis thaliana
), rice
(Oryza sativa
), and an early evolution
ary 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 eukaryote
s probably have experienced a polyploidy event at some point in their evolutionary history.
complement of a eukaryote
species
. The preparation and study of karyotypes is part of cytology
and, more specifically, cytogenetics
.
Although the replication and transcription of DNA is highly standardized in eukaryotes, the same cannot be said for their karotypes, which are highly variable between species in chromosome number and in detailed organization despite being constructed out of the same macromolecules. In some cases there is even significant variation within species. This variation provides the basis for a range of studies in what might be called evolutionary cytology.
, copy and paste transposons, or whole genome duplications.
and meiosis
. In a diploid, one homolog is derived from the male parent (sperm) and one is derived from the female parent (egg). During meiosis and gametogenesis
, homologous chromosomes pair and exchange genetic material by recombination
, leading to the production of sperm or eggs with chromosome haplotypes containing novel genetic variation.
, leading to disomic inheritance; however in some allopolyploids, the homoeologous chromosomes of the parental genomes may be nearly as similar to one another as the homologous chromosomes, leading to tetrasomic inheritance (four chromosomes pairing at meiosis), intergenomic recombination
, and reduced fertility.
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s containing more than two paired (homologous
Homologous chromosome
Homologous chromosomes are chromosome pairs of approximately the same length, centromere position, and staining pattern, with genes for the same characteristics at corresponding loci. One homologous chromosome is inherited from the organism's mother; the other from the organism's father...
) sets of chromosomes. Most eukaryotic
Eukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...
species are diploid, meaning they have two sets of chromosomes — one set inherited from each parent. However polyploidy is found in some organisms and is especially common in plants. In addition, polyploidy also occurs in some tissues of animals who are otherwise diploid, such as human muscle tissues. This is known as endopolyploidy. (Monoploid
Ploidy
Ploidy is the number of sets of chromosomes in a biological cell.Human sex cells have one complete set of chromosomes from the male or female parent. Sex cells, also called gametes, combine to produce somatic cells. Somatic cells, therefore, have twice as many chromosomes. The haploid number is...
organisms also occur; a monoploid has only one set of chromosomes. These include the vast majority of prokaryotes.)
Polyploidy refers to a numerical change in a whole set of chromosomes. Organisms in which a particular chromosome, or chromosome segment, is under- or overrepresented are said to be aneuploid
Aneuploidy
Aneuploidy is an abnormal number of chromosomes, and is a type of chromosome abnormality. An extra or missing chromosome is a common cause of genetic disorders . Some cancer cells also have abnormal numbers of chromosomes. Aneuploidy occurs during cell division when the chromosomes do not separate...
(from the Greek words meaning "not," "good," and "fold"). Therefore the distinction between aneuploidy and polyploidy is that aneuploidy refers to a numerical change in part of the chromosome set, whereas polyploidy refers to a numerical change in the whole set of chromosomes.
Polyploidy may occur due to abnormal cell division
Cell division
Cell division is the process by which a parent cell divides into two or more daughter cells . Cell division is usually a small segment of a larger cell cycle. This type of cell division in eukaryotes is known as mitosis, and leaves the daughter cell capable of dividing again. The corresponding sort...
, either during mitosis
Mitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
, or commonly during metaphase I in meiosis
Meiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
.
Polyploidy occurs in some animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
s, such as goldfish
Goldfish
The goldfish is a freshwater fish in the family Cyprinidae of order Cypriniformes. It was one of the earliest fish to be domesticated, and is one of the most commonly kept aquarium fish....
, salmon
Salmon
Salmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...
, and salamander
Salamander
Salamander is a common name of approximately 500 species of amphibians. They are typically characterized by a superficially lizard-like appearance, with their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant...
s, but is especially common among fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s and flowering plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s (see Hibiscus rosa-sinensis), including both wild and cultivated species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
. Wheat
Wheat
Wheat is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...
, 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
Durum wheat or macaroni wheat is the only tetraploid species of wheat of commercial importance that is widely cultivated today...
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
Brassica is a genus of plants in the mustard family . The members of the genus may be collectively known either as cabbages, or as mustards...
are also tetraploids. Polyploidization is a mechanism of sympatric speciation
Sympatric speciation
Sympatric speciation is the process through which new species evolve from a single ancestral species while inhabiting the same geographic region. In evolutionary biology and biogeography, sympatric and sympatry are terms referring to organisms whose ranges overlap or are even identical, so that...
because polyploids are usually unable to interbreed with their diploid ancestors.
Polyploidy can be induced in plants and cell culture
Cell culture
Cell culture is the complex process by which cells are grown under controlled conditions. In practice, the term "cell culture" has come to refer to the culturing of cells derived from singlecellular eukaryotes, especially animal cells. However, there are also cultures of plants, fungi and microbes,...
s by some chemicals: the best known is colchicine
Colchicine
Colchicine is a medication used for gout. It is a toxic natural product and secondary metabolite, originally extracted from plants of the genus Colchicum...
, which can result in chromosome doubling, though its use may have other less obvious consequences as well. Oryzalin
Oryzalin
Oryzalin is an herbicide. It acts through the disruption of microtubules, thus blocking anisotropic growth of plant cells....
also will double the existing chromosome content.
Polyploid types
Polyploid types are labeled according to the number of chromosome sets in the nucleusCell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
:
- triploid (three sets; 3x), for example seedless watermelonsParthenocarpyIn botany and horticulture, parthenocarpy is the natural or artificially induced production of fruit without fertilization of ovules. The fruit is therefore seedless. Stenospermocarpy may also produce apparently seedless fruit, but the seeds are actually aborted while still small...
, common in the phylumPhylumIn biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....
Tardigrada - tetraploid (four sets; 4x), for example SalmonidaeSalmonidaeSalmonidae is a family of ray-finned fish, the only living family currently placed in the order Salmoniformes. It includes salmon, trout, chars, freshwater whitefishes and graylings...
fish - pentaploid (five sets; 5x), for example Kenai Birch (Betula papyrifera var. kenaica)
- hexaploid (six sets; 6x), for example wheatWheatWheat is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...
, kiwifruitKiwifruitThe kiwifruit, often shortened to kiwi in many parts of the world, is the edible berry of a cultivar group of the woody vine Actinidia deliciosa and hybrids between this and other species in the genus Actinidia.... - octaploid (eight sets; 8x), for example AcipenserAcipenserAcipenser is genus of sturgeons. With about 19 species, many of which are threatened, it is the largest genus in the order Acipenseriformes.-Species:*Acipenser baerii J. F. Brandt, 1869**Acipenser baerii baerii J. F...
(genus of sturgeonSturgeonSturgeon is the common name used for some 26 species of fish in the family Acipenseridae, including the genera Acipenser, Huso, Scaphirhynchus and Pseudoscaphirhynchus. The term includes over 20 species commonly referred to as sturgeon and several closely related species that have distinct common...
fish), dahlias - decaploid (ten sets; 10x), for example certain strawberries
- dodecaploid (twelve sets; 12x), for example the plant Celosia argenteaCelosia argenteaCelosia argentea, commonly known as plumed cockscomb, is a plant of tropical origin, and is known for its very bright colors.-Description:...
and the amphibian Xenopus ruwenzoriensis
Polyploidy in animals
Examples in animals are more common in the 'lower' forms such as flatwormFlatworm
The flatworms, known in scientific literature as Platyhelminthes or Plathelminthes are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrate animals...
s, leech
Leech
Leeches are segmented worms that belong to the phylum Annelida and comprise the subclass Hirudinea. Like other oligochaetes such as earthworms, leeches share a clitellum and are hermaphrodites. Nevertheless, they differ from other oligochaetes in significant ways...
es, and brine shrimp
Brine shrimp
Artemia is a genus of aquatic crustaceans known as brine shrimp. Artemia, the only genus in the family Artemiidae, has changed little externally since the Triassic period...
. Polyploid animals are often sterile, so they often reproduce by parthenogenesis
Parthenogenesis
Parthenogenesis is a form of asexual reproduction found in females, where growth and development of embryos occur without fertilization by a male...
. Polyploid lizards are also quite common and parthenogenetic. Polyploid mole salamanders (mostly triploids) are all female and reproduce by kleptogenesis, "stealing" spermatophore
Spermatophore
A spermatophore or sperm ampulla is a capsule or mass created by males of various animal species, containing spermatozoa and transferred in entirety to the female's ovipore during copulation...
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 are known, but most often result in prenatal death.
An octodontid
Octodontidae
The Octodontidae are a family of rodents, restricted to south-western South America. Thirteen species of octodontid are recognised, arranged in nine genera. The best known species is the Degu, Octodon degus....
rodent
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
of Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
's harsh desert
Desert
A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Most deserts have an average annual precipitation of less than...
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. The rodent is not a rat
Rat
Rats are various medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and the brown rat, Rattus norvegicus...
, but kin to guinea pig
Guinea pig
The guinea pig , also called the cavy, is a species of rodent belonging to the family Caviidae and the genus Cavia. Despite their common name, these animals are not in the pig family, nor are they from Guinea...
s and chinchilla
Chinchilla
Chinchillas are crepuscular rodents, slightly larger and more robust than ground squirrels, and are native to the Andes mountains in South America. Along with their relatives, viscachas, they make up the family Chinchillidae....
s. Its "new" diploid [2n] number is 102 and so its cells are roughly twice normal size. Its closest living relation is Octomys mimax, the Andean
Andes
The Andes is the world's longest continental mountain range. It is a continual range of highlands along the western coast of South America. This range is about long, about to wide , and of an average height of about .Along its length, the Andes is split into several ranges, which are separated...
Viscacha-Rat of the same family, whose 2n = 56. It was therefore surmised that an Octomys-like ancestor produced tetraploid (i.e., 4n = 112) offspring that were, by virtue of their doubled chromosomes, reproductively isolated from their parents.
Polyploidy in humans
True polyploidy rarely occurs in humans, although it occurs in some tissues (especially in the liver). AneuploidyAneuploidy
Aneuploidy is an abnormal number of chromosomes, and is a type of chromosome abnormality. An extra or missing chromosome is a common cause of genetic disorders . Some cancer cells also have abnormal numbers of chromosomes. Aneuploidy occurs during cell division when the chromosomes do not separate...
is more common.
Polyploidy occurs in humans in the form of triploidy, with 69 chromosomes (sometimes called 69,XXX), and tetraploidy with 92 chromosomes (sometimes called 92,XXXX). Triploidy, usually due to polyspermy
Polyspermy
In biology, polyspermy describes an egg that has been fertilized 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 more copies of each chromosome -- one from the...
, occurs in about 2–3% of all human pregnancies and ~15% of miscarriages. The vast majority of triploid conceptions end as miscarriage
Miscarriage
Miscarriage or spontaneous abortion is the spontaneous end of a pregnancy at a stage where the embryo or fetus is incapable of surviving independently, generally defined in humans at prior to 20 weeks of gestation...
and those that do survive to term typically die shortly after birth. In some cases survival past birth may occur longer if there is mixoploidy with both a diploid and a triploid cell population present.
Triploidy may be the result of either digyny (the extra haploid set is from the mother) or diandry (the extra haploid set is from the father). Diandry is mostly caused by reduplication of the paternal haploid set from a single sperm, but may also be the consequence of dispermic (two sperm) fertilization of the egg. Digyny is most commonly caused by either failure of one meiotic division during oogenesis leading to a diploid oocyte
Oocyte
An oocyte, ovocyte, or rarely ocyte, 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 the ovary during female gametogenesis. The female germ cells produce a primordial germ cell which undergoes a mitotic...
or failure to extrude one polar body
Polar body
A polar body is a cell structure found inside an ovum. Both animal and plant ova possess it. It is also known as a polar cell.Asymmetrical cell division leads to the production of polar bodies during oogenesis. To conserve nutrients, the majority of cytoplasm is segregated into the secondary...
from the oocyte
Oocyte
An oocyte, ovocyte, or rarely ocyte, 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 the ovary during female gametogenesis. The female germ cells produce a primordial germ cell which undergoes a mitotic...
. Diandry appears to predominate among early miscarriage
Miscarriage
Miscarriage or spontaneous abortion is the spontaneous end of a pregnancy at a stage where the embryo or fetus is incapable of surviving independently, generally defined in humans at prior to 20 weeks of gestation...
s while digyny predominates among triploidy that survives into the fetal period. However, among early miscarriages, digyny is also more common in those cases <8.5 weeks gestational age or those in which an embryo is present. There are also two distinct phenotype
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
s in triploid placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
s and fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
es that are dependent on the origin of the extra haploid set. In digyny there is typically an asymmetric poorly grown fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
, with marked adrenal hypoplasia
Hypoplasia
Hypoplasia is underdevelopment or incomplete development of a tissue or organ. Although the term is not always used precisely, it properly refers to an inadequate or below-normal number of cells. Hypoplasia is similar to aplasia, but less severe. It is technically not the opposite of hyperplasia...
and a very small placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
. In diandry, a partial hydatidiform mole
Hydatidiform mole
Molar pregnancy is an abnormal form of pregnancy, wherein a non-viable, fertilized egg implants in the uterus, and thereby converts normal pregnancy processes into pathological ones. It is characterized by the presence of a hydatidiform mole...
develops. These parent-of-origin effects reflect the effects of genomic imprinting
Imprinting (genetics)
Genomic imprinting is a genetic phenomenon by which certain genes are expressed in a parent-of-origin-specific manner. It is an inheritance process independent of the classical Mendelian inheritance. Imprinted alleles are silenced such that the genes are either expressed only from the non-imprinted...
.
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 diagnosis
Prenatal diagnosis or prenatal screening is testing for diseases or conditions in a fetus or embryo before it is born. The aim is to detect birth defects such as neural tube defects, Down syndrome, chromosome abnormalities, genetic diseases and other conditions, such as spina bifida, cleft palate,...
and these are generally considered 'harmless'. It is not clear whether these tetraploid cells simply tend to arise during in vitro cell culture or whether they are also present in placental cells in vivo. There are, at any rate, very few clinical reports of fetuses/infants diagnosed with tetraploidy mosaicism.
Mixoploidy is quite commonly observed in human preimplantation embryos and includes haploid/diploid as well as diploid/tetraploid mixed cell populations. It is unknown whether these embryos fail to implant and are therefore rarely detected in ongoing pregnancies or if there is simply a selective process favoring the diploid cells.
Polyploidy in plants
Paleopolyploidy
Paleopolyploidy refers to ancient genome duplications which occurred at least several million years ago . The genome doubling event could either be an autopolyploidy or an allopolyploidy. Due to functional redundancy, genes are rapidly silenced and/or lost from the duplicated genomes...
) 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 (2n) gametes. Both autopolyploids (e.g. potato) and allopolyploids (e.g. canola, wheat, cotton) can be found among both wild and domesticated plant species. Most polyploids display heterosis
Heterosis
Heterosis, or hybrid vigor, or outbreeding enhancement, is the improved or increased function of any biological quality in a hybrid offspring. The adjective derived from heterosis is heterotic....
relative to their parental species, and may display novel variation or morphologies that may contribute to the processes of speciation
Speciation
Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...
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.
Lomatia tasmanica is an extremely rare Tasmanian shrub which is triploid and sterile, and reproduction is entirely vegetative with all plants having the same genetic structure.
There are few naturally occurring polyploid conifers. One example is the giant tree
Tree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...
Sequoia sempervirens or Coast Redwood which is a hexaploid (6x) with 66 chromosomes (2n = 6x = 66), although the origin is unclear.
Polyploid crops
The induction of polyploidy is a common technique to overcome the sterility of a hybrid species during plant breeding. For example, TriticaleTriticale
Triticale is a hybrid of wheat and rye first bred in laboratories during the late 19th century. The grain was originally bred in Scotland and Sweden. Commercially available triticale is almost always a second generation hybrid, i.e., a cross between two kinds of primary triticales...
is the hybrid of wheat (Triticum turgidum) and rye
Rye
Rye is a grass grown extensively as a grain and as a forage crop. It is a member of the wheat tribe and is closely related to barley and wheat. Rye grain is used for flour, rye bread, rye beer, some whiskeys, some vodkas, and animal fodder...
(Secale cereale). It combines sought-after characteristics of the parents, but the initial hybrids are sterile. After polyploidization, the hybrid becomes fertile and can thus be further propagated to become triticale.
In some situations polyploid crops are preferred because they are sterile. For example many seedless fruit varieties are seedless as a result of polyploidy. Such crops are propagated using asexual techniques such as grafting.
Polyploidy in crop plants is most commonly induced by treating seeds with the chemical colchicine.
Examples of polyploid crops
- Triploid crops: appleAppleThe apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family . It is one of the most widely cultivated tree fruits, and the most widely known of the many members of genus Malus that are used by humans. Apple grow on small, deciduous trees that blossom in the spring...
, bananaBananaBanana is the common name for herbaceous plants of the genus Musa and for the fruit they produce. Bananas come in a variety of sizes and colors when ripe, including yellow, purple, and red....
, citrusCitrusCitrus is a common term and genus of flowering plants in the rue family, Rutaceae. Citrus is believed to have originated in the part of Southeast Asia bordered by Northeastern India, Myanmar and the Yunnan province of China...
, gingerGingerGinger is the rhizome of the plant Zingiber officinale, consumed as a delicacy, medicine, or spice. It lends its name to its genus and family . Other notable members of this plant family are turmeric, cardamom, and galangal....
, watermelonWatermelonWatermelon is a vine-like flowering plant originally from southern Africa. Its fruit, which is also called watermelon, is a special kind referred to by botanists as a pepo, a berry which has a thick rind and fleshy center... - Tetraploid crops: appleAppleThe apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family . It is one of the most widely cultivated tree fruits, and the most widely known of the many members of genus Malus that are used by humans. Apple grow on small, deciduous trees that blossom in the spring...
, durumDurumDurum wheat or macaroni wheat is the only tetraploid species of wheat of commercial importance that is widely cultivated today...
or macaroniMacaroniMacaroni is a variety of moderately extended, machine-made, dry pasta made with durum wheat. Macaroni noodles do not contain eggs, and are normally cut in short, hollow shapes; however, the term refers not to the shape of the pasta, but to the kind of dough from which the noodle is made...
wheatWheatWheat is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...
, cottonCottonCotton is a soft, fluffy staple fiber that grows in a boll, or protective capsule, around the seeds of cotton plants of the genus Gossypium. The fiber is almost pure cellulose. The botanical purpose of cotton fiber is to aid in seed dispersal....
, potatoPotatoThe potato is a starchy, tuberous crop from the perennial Solanum tuberosum of the Solanaceae family . The word potato may refer to the plant itself as well as the edible tuber. In the region of the Andes, there are some other closely related cultivated potato species...
, cabbageCabbageCabbage is a popular cultivar of the species Brassica oleracea Linne of the Family Brassicaceae and is a leafy green vegetable...
, leek, tobaccoTobaccoTobacco is an agricultural product processed from the leaves of plants in the genus Nicotiana. It can be consumed, used as a pesticide and, in the form of nicotine tartrate, used in some medicines...
, peanutPeanutThe peanut, or groundnut , is a species in the legume or "bean" family , so it is not a nut. The peanut was probably first cultivated in the valleys of Peru. It is an annual herbaceous plant growing tall...
, kinnowKinnowThe kinnow is a variety of citrus fruit cultivated extensively in India and Pakistani Punjab Province. It is a hybrid of two citrus cultivars — "King" x "Willow Leaf" — first developed by H. B. Frost at the Citrus Research Centre of the University of California, Riverside, USA...
, PelargoniumPelargoniumPelargonium is a genus of flowering plants which includes about 200 species of perennials, succulents, and shrubs, commonly known as scented geraniums or storksbills. Confusingly, Geranium is the correct botanical name of a separate genus of related plants often called Cranesbills. Both Geranium... - Hexaploid crops: chrysanthemumChrysanthemumChrysanthemums, often called mums or chrysanths, are of the genus constituting approximately 30 species of perennial flowering plants in the family Asteraceae which is native to Asia and northeastern Europe.-Etymology:...
, bread wheatWheatWheat is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...
, triticaleTriticaleTriticale is a hybrid of wheat and rye first bred in laboratories during the late 19th century. The grain was originally bred in Scotland and Sweden. Commercially available triticale is almost always a second generation hybrid, i.e., a cross between two kinds of primary triticales...
, oatOatThe common oat is a species of cereal grain grown for its seed, which is known by the same name . While oats are suitable for human consumption as oatmeal and rolled oats, one of the most common uses is as livestock feed...
, kiwifruitKiwifruitThe kiwifruit, often shortened to kiwi in many parts of the world, is the edible berry of a cultivar group of the woody vine Actinidia deliciosa and hybrids between this and other species in the genus Actinidia.... - Octaploid crops: strawberryStrawberryFragaria is a genus of flowering plants in the rose family, Rosaceae, commonly known as strawberries for their edible fruits. Although it is commonly thought that strawberries get their name from straw being used as a mulch in cultivating the plants, the etymology of the word is uncertain. There...
, dahliaDahliaDahlia is a genus of bushy, tuberous, perennial plants native to Mexico, Central America, and Colombia. There are at least 36 species of dahlia, some like D. imperialis up to 10 metres tall. Dahlia hybrids are commonly grown as garden plants...
, pansies, sugar cane, oca (Oxalis tuberosa)
Some crops are found in a variety of ploidies: tulip
Tulip
The tulip is a perennial, bulbous plant with showy flowers in the genus Tulipa, which comprises 109 species and belongs to the family Liliaceae. The genus's native range extends from as far west as Southern Europe, North Africa, Anatolia, and Iran to the Northwest of China. The tulip's centre of...
s and lilies are commonly found as both diploid and as triploid; daylilies (Hemerocallis cultivars) are available as either diploid or tetraploid; apples and kinnow
Kinnow
The kinnow is a variety of citrus fruit cultivated extensively in India and Pakistani Punjab Province. It is a hybrid of two citrus cultivars — "King" x "Willow Leaf" — first developed by H. B. Frost at the Citrus Research Centre of the University of California, Riverside, USA...
s can be diploid, triploid, or tetraploid.
Autopolyploidy
Autopolyploids are polyploids with multiple chromosome sets derived from a single species. Autopolyploids can arise from a spontaneous, naturally occurring genomeGenome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
doubling, like the potato. Others might form following fusion of 2n gametes (unreduced gametes). Bananas and apples can be found as autotriploids. Autopolyploid plants typically display polysomic inheritance, and are therefore often infertile and propagated clonally perfect.
Allopolyploidy
Allopolyploids are polyploids with chromosomes derived from different species. Precisely it is the result of doubling of chromosome number in an F1 hybrid. TriticaleTriticale
Triticale is a hybrid of wheat and rye first bred in laboratories during the late 19th century. The grain was originally bred in Scotland and Sweden. Commercially available triticale is almost always a second generation hybrid, i.e., a cross between two kinds of primary triticales...
is an example of an allopolyploid, having six chromosome sets, allohexaploid, four from wheat (Triticum turgidum) and two from rye (Secale cereale). Amphidiploid is another word for an allopolyploid. Some of the best examples of allopolyploids come from the Brassicas, and the Triangle of U
Triangle of U
The Triangle of U is a theory about the evolution and relationships between members of the plant genus Brassica. The theory states that the genomes of three ancestral species of Brassica combined to create three of the common contemporary vegetables and oilseed crop species...
describes the relationships among the three common diploid Brassicas (B. oleracea, B. rapa, and B. nigra) and three allotetraploids (B. napus, B. juncea, and B. carinata) derived from hybridization among the diploids.
Paleopolyploidy
Ancient genome duplications probably occurred in the evolutionary history of all life. Duplication events that occurred long ago in the history of various evolutionary lineagesLineage (evolution)
An evolutionary lineage is a sequence of species, that form a line of descent, each new species the direct result of speciation from an immediate ancestral species. Lineages are subsets of the evolutionary tree of life. Lineages are often determined by the techniques of molecular systematics.-...
can be difficult to detect because of subsequent diploidization (such that a polyploid starts to behave cytogenetically as a diploid over time) as mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
s and gene translations gradually make one copy of each chromosome unlike its other copy.
In many cases, these events can be inferred only through comparing sequenced genomes
DNA sequencing
DNA sequencing includes several methods and technologies that are used for determining the order of the nucleotide bases—adenine, guanine, cytosine, and thymine—in a molecule of DNA....
. Examples of unexpected but recently confirmed ancient genome duplications include baker's yeast
Baker's yeast
Baker's yeast is the common name for the strains of yeast commonly used as a leavening agent in baking bread and bakery products, where it converts the fermentable sugars present in the dough into carbon dioxide and ethanol...
(Saccharomyces cerevisiae
Saccharomyces cerevisiae
Saccharomyces cerevisiae is a species of yeast. It is perhaps the most useful yeast, having been instrumental to baking and brewing since ancient times. It is believed that it was originally isolated from the skin of grapes...
), mustard weed/thale cress (Arabidopsis thaliana
Arabidopsis thaliana
Arabidopsis thaliana is a small flowering plant native to Europe, Asia, and northwestern Africa. A spring annual with a relatively short life cycle, arabidopsis is popular as a model organism in plant biology and genetics...
), rice
Rice
Rice is the seed of the monocot plants Oryza sativa or Oryza glaberrima . As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East Asia, Southeast Asia, South Asia, the Middle East, and the West Indies...
(Oryza sativa
Oryza sativa
Oryza sativa, commonly known as Asian rice, is the plant species most commonly referred to in English as rice. Oryza sativa is the cereal with the smallest genome, consisting of just 430Mb across 12 chromosomes...
), and an early evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
ary ancestor
Ancestor
An ancestor is a parent or the parent of an ancestor ....
of the vertebrates (which includes the human
Human
Humans are the only living species in the Homo genus...
lineage) and another near the origin of the teleost fishes. Angiosperms (flowering plants) have paleopolyploidy in their ancestry. All eukaryote
Eukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...
s probably have experienced a polyploidy event at some point in their evolutionary history.
Karyotype
A karyotype is the characteristic chromosomeChromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
complement of a eukaryote
Eukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...
species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
. The preparation and study of karyotypes is part of cytology
Cytopathology
Cytopathology is a branch of pathology that studies and diagnoses diseases on the cellular level. The discipline was founded by Rudolf Virchow in 1858. A common application of cytopathology is the Pap smear, used as a screening tool, to detect precancerous cervical lesions and prevent cervical...
and, more specifically, cytogenetics
Cytogenetics
Cytogenetics is a branch of genetics that is concerned with the study of the structure and function of the cell, especially the chromosomes. It includes routine analysis of G-Banded chromosomes, other cytogenetic banding techniques, as well as molecular cytogenetics such as fluorescent in situ...
.
Although the replication and transcription of DNA is highly standardized in eukaryotes, the same cannot be said for their karotypes, which are highly variable between species in chromosome number and in detailed organization despite being constructed out of the same macromolecules. In some cases there is even significant variation within species. This variation provides the basis for a range of studies in what might be called evolutionary cytology.
Paralogous
The term is used to describe the relationship among duplicated genes or portions of chromosomes that derived from a common ancestral DNA. Paralogous segments of DNA may arise spontaneously by errors during DNA replicationDNA replication
DNA replication is a biological process that occurs in all living organisms and copies their DNA; it is the basis for biological inheritance. The process starts with one double-stranded DNA molecule and produces two identical copies of the molecule...
, copy and paste transposons, or whole genome duplications.
Homologous
The term is used to describe the relationship of similar chromosomes that pair at mitosisMitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
and meiosis
Meiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
. In a diploid, one homolog is derived from the male parent (sperm) and one is derived from the female parent (egg). During meiosis and gametogenesis
Gametogenesis
Gametogenesis is a biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes. Depending on the biological life cycle of the organism, gametogenesis occurs by meiotic division of diploid gametocytes into various gametes,...
, homologous chromosomes pair and exchange genetic material by recombination
Genetic recombination
Genetic recombination is a process by which a molecule of nucleic acid is broken and then joined to a different one. Recombination can occur between similar molecules of DNA, as in homologous recombination, or dissimilar molecules, as in non-homologous end joining. Recombination is a common method...
, leading to the production of sperm or eggs with chromosome haplotypes containing novel genetic variation.
Homoeologous
The term homoeologous, also spelled homeologous, is used to describe the relationship of similar chromosomes or parts of chromosomes brought together following inter-species hybridization and allopolyploidization, and whose relationship was completely homologous in an ancestral species. In allopolyploids, the homologous chromosomes within each parental sub-genome should pair faithfully during meiosisMeiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
, leading to disomic inheritance; however in some allopolyploids, the homoeologous chromosomes of the parental genomes may be nearly as similar to one another as the homologous chromosomes, leading to tetrasomic inheritance (four chromosomes pairing at meiosis), intergenomic recombination
Genetic recombination
Genetic recombination is a process by which a molecule of nucleic acid is broken and then joined to a different one. Recombination can occur between similar molecules of DNA, as in homologous recombination, or dissimilar molecules, as in non-homologous end joining. Recombination is a common method...
, and reduced fertility.
Example of homoeologous chromosomes
Durum wheat is the result of the inter-species hybridization of two diploid grass species Triticum urartu and Aegilops speltoides. Both the diploid ancestors had two sets of 7 chromosomes, which were similar in terms of size and genes contained on them. Durum wheat contains two sets of chromosomes derived from Triticum urartu and two sets of chromosomes derived from Aegilops speltoides. Each chromosome pair derived from the Triticum urartu parent is homoeologous to the opposite chromosome pair derived from the Aegilops speltoides parent, though each chromosome pair unto itself is homologous.See also
- ChromosomeChromosomeA chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
- KaryotypeKaryotypeA karyotype is the number and appearance of chromosomes in the nucleus of an eukaryotic cell. The term is also used for the complete set of chromosomes in a species, or an individual organism.p28...
- MeiosisMeiosisMeiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
- PaleopolyploidyPaleopolyploidyPaleopolyploidy refers to ancient genome duplications which occurred at least several million years ago . The genome doubling event could either be an autopolyploidy or an allopolyploidy. Due to functional redundancy, genes are rapidly silenced and/or lost from the duplicated genomes...
- Polyploid complexPolyploid complexA polyploid complex is a group of interrelated and interbreeding plants that also have differing levels of ploidy that can allow genetic exchanges between unrelated species.The polyploid complex was first described by E. B. Babcock and G...
- SpeciationSpeciationSpeciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...
- SympatrySympatryIn biology, two species or populations are considered sympatric when they exist in the same geographic area and thus regularly encounter one another. An initially-interbreeding population that splits into two or more distinct species sharing a common range exemplifies sympatric speciation...
Further reading
- Snustad, P. et al. 2006. Principles of Genetics, 4th ed. John Wiley & Sons, Inc. Hoboken, NJ ISBN 100-471-69939-X
- Gregory, T.R. & Mable, B.K. (2005). Polyploidy in animals. In The Evolution of the GenomeThe Evolution of the GenomeThe Evolution of the Genome is a book edited by Dr. T. Ryan Gregory of the University of Guelph, in Guelph, Ontario, Canada, covering a wide range of topics in the study of genome evolution...
(edited by T.R. Gregory). Elsevier, San Diego, pp. 427–517. - Tate, J.A., Soltis, D.E., & Soltis, P.S. (2005). Polyploidy in plants. In The Evolution of the GenomeThe Evolution of the GenomeThe Evolution of the Genome is a book edited by Dr. T. Ryan Gregory of the University of Guelph, in Guelph, Ontario, Canada, covering a wide range of topics in the study of genome evolution...
(edited by T.R. Gregory). Elsevier, San Diego, pp. 371–426. - Van de Peer, Y. and Meyer, A. (2005). Large-scale gene and ancient genome duplications. In The Evolution of the GenomeThe Evolution of the GenomeThe Evolution of the Genome is a book edited by Dr. T. Ryan Gregory of the University of Guelph, in Guelph, Ontario, Canada, covering a wide range of topics in the study of genome evolution...
(edited by T.R. Gregory). Elsevier, San Diego, pp. 329–368
External links
- Polyploidy on Kimball's Biology Pages
- The polyploidy portal a community-editable project with information, research, education, and a bibliography about polyploidy.