Ploidy refers to the number of sets of chromosomes A chromosome is an organized structure of DNA and protein that is 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. The word chromosome comes from the Greek χρῶμα in a biological cell The cell is the functional basic unit of life. It was discovered by Robert Hooke and is the functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. Some organisms, such as most bacteria, are unicellular . Other organisms, such as humans,.
Human germ cells (sperm and egg An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization. In lower plants and algae, the ovum is also often called oosphere) have one complete set of chromosomes from the male or female parent. Germ cells, also called gametes A gamete is a cell that fuses with another gamete during fertilization (conception) in organisms that reproduce sexually. In species that produce two morphologically distinct types of gametes, and in which each individual produces only one type, a female is any individual that produces the larger type of gamete—called an ovum (or egg)—and a, combine to produce somatic cells Somatic cells are any cells forming the body of an organism, as opposed to germline cells. In mammals, germline cells (also known as "gametes") are the spermatozoa and ova which fuse during fertilization to produce a cell called a zygote, from which the entire mammalian embryo develops. Every other cell type in the mammalian body—apart. Somatic cells therefore have twice as many chromosomes. The haploid number (n) is the number of chromosomes in a gamete. A somatic cell has twice that many chromosomes (2n).
Humans are diploid. A human somatic cell contains 46 chromosomes: 2 complete haploid sets, which make up 23 homologous A homologous[Etymology 1] trait is any characteristic of organisms that is derived from a common ancestor. This is contrasted to analagous traits: similarities between organisms that were not in the last common ancestor of the taxa being considered but rather evolved separately. As defined by Owen , a homology is a "structural correspondence& chromosome pairs. However, many organisms have more than two sets of homologous chromosomes and are called polyploid Polyploidy occurs in cells and organisms when there are more than two paired sets of chromosomes.
The number of chromosomes in a single (non-homologous) set is called the monoploid number (x), and is different from the haploid number (n). Both numbers n, and x, apply to every cell of a given organism. For humans, x = n = 23, which is also written as 2n = 2x = 46. Bread wheat Bread wheat is an allohexaploid . Free-threshing wheat is closely related to spelt. As with spelt, genes contributed from goatgrass (Aegilops tauschii) give bread wheat greater cold hardiness than most wheats, and it is cultivated throughout the world's temperate regions is an organism where x and n differ. It has six sets of chromosomes, two sets from each of three different diploid species that are its distant ancestors. The somatic cells are hexaploid, with six sets of chromosomes, 2n = 6x = 42. The gametes are both haploid and triploid, with three sets of chromosomes. The monoploid number x = 7, and the haploid number n = 21.
Tetraploidy (four sets of chromosomes, 2n=4x) is common in plants Plants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants, known as botany, has identified about 350,000 extant species of plants, defined as seed plants, bryophytes, ferns and fern allies. As of 2004,, and also occurs in amphibians Amphibians , such as frogs, toads, salamanders, newts, and caecilians, are ectothermic (or cold-blooded) animals that metamorphose from a juvenile water-breathing form, either to an adult air-breathing form, or to a paedomorph that retains some juvenile characteristics. Proteidae (mudpuppies and waterdogs) are good examples of paedomorphic species, reptiles Reptiles are animals in the class Reptilia characterized by breathing air, a "cold-blooded" (poikilothermic) metabolism, laying tough-shelled amniotic eggs (or retaining the same membrane system in species with live birth), and skin with scales or scutes. They are tetrapods (either having four limbs or being descended from four-limbed, and insects Insects are a class within the arthropods that have a chitinous exoskeleton, a three-part body (head, thorax, and abdomen), three pairs of jointed legs, compound eyes, and two antennae. They are among the most diverse group of animals on the planet and include more than a million described species and represent more than half of all known living.
The Australian bulldog ant, Myrmecia pilosula The jack jumper ant, hopper ant, jumper ant or jumping jack, Myrmecia pilosula, is a species of bulldog ant that is native to Australia. The ants are recorded throughout the country, but are most often found in Tasmania, rural Victoria, New South Wales, Australian Capital Territory and the southeast area of South Australia, a haplodiploid species, has n = x = 1, the lowest chromosome number theoretically possible[1]. Haploid individuals of this species have a single chromosome, and diploid individuals have two chromosomes.
Euploidy is the state of a cell or organism having an integral multiple of the monoploid number, possibly excluding the sex-determining chromosomes. For example, a human cell has 46 chromosomes, which is an integer The integers are formed by the natural numbers including 0 (0, 1, 2, 3, ...) together with the negatives of the non-zero natural numbers (−1, −2, −3, ...). Viewed as subset of the real numbers, they are numbers that can be written without a fractional or decimal component, and fall within the set {... −2, −1, 0, 1, 2, ...}. For example, 6 multiple of the monoploid number, 23. A human with abnormal, but integral, multiples of this full set (e.g. 69 chromosomes) would also be considered as euploid. 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 properly between the two cells. Chromosome is the state of not having euploidy. In humans, examples include having a single extra chromosome (such as Down syndrome Down syndrome, or Down's syndrome , trisomy 21, or trisomy G, is a chromosomal disorder caused by the presence of all or part of an extra 21st chromosome. It is named after John Langdon Down, the British physician who described the syndrome in 1866. The disorder was identified as a chromosome 21 trisomy by Jérôme Lejeune in 1959. The condition), or missing a chromosome (such as Turner syndrome Turner syndrome or Ullrich-Turner syndrome encompasses several conditions, of which monosomy X (absence of an entire sex chromosome) is most common. It is a chromosomal abnormality in which all or part of one of the sex chromosomes is absent (unaffected humans have 46 chromosomes, of which two are sex chromosomes). Typical females have two X). Aneuploid karyotypes A karyotype is the number and appearance of chromosomes in the nucleus of a eukaryote cell.p28 The term is also used for the complete set of chromosomes in a species, or an individual organism are given names with the suffix -somy (rather than -ploidy, used for euploid karyotypes), such as trisomy A trisomy is a genetic abnormality in which there are three copies, instead of the normal two, of a particular chromosome. A trisomy is a type of aneuploidy and monosomy Monosomy is a form of aneuploidy with the presence of only one chromosome from a pair. Partial monosomy occurs when only a portion of the chromosome has one copy, while the rest has two copies.
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Haploid and monoploid
As stated above, the haploid number (n) is the number of chromosomes in a gamete A gamete is a cell that fuses with another gamete during fertilization (conception) in organisms that reproduce sexually. In species that produce two morphologically distinct types of gametes, and in which each individual produces only one type, a female is any individual that produces the larger type of gamete—called an ovum (or egg)—and a of an individual, and this is distinct from the monoploid number (x) which is the number of unique chromosomes in a single complete set. Gametes (sperm, and ova An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization. In lower plants and algae, the ovum is also often called oosphere) are haploid cells. The haploid gametes produced by (most) diploid organisms are monoploid, and these can combine to form a diploid zygote A zygote , or zygocyte, is the initial cell formed when a new organism is produced by means of sexual reproduction. A zygote is synthesized from the union of two gametes, and constitutes the first stage in a unique organism's development. Zygotes are usually produced by a fertilization event between two haploid cells — an ovum from a female and. For example, most animals are diploid and produce monoploid gametes.
During meiosis In biology, meiosis (pronounced maɪˈoʊsɨs ) is a process of reductional division in which the number of chromosomes per cell is cut in half. In animals, meiosis always results in the formation of gametes, while in other organisms it can give rise to spores. As with mitosis, before meiosis begins, the DNA in the original cell is replicated, germ cell precursors have their number of chromosomes halved by randomly "choosing" one homologue, resulting in haploid gametes. Because homologous chromosomes usually differ genetically, gametes usually differ genetically from one another.
All plants Plants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants, known as botany, has identified about 350,000 extant species of plants, defined as seed plants, bryophytes, ferns and fern allies. As of 2004, and many fungi and algae switch between a haploid and a diploid state (which may be polyploid Polyploidy occurs in cells and organisms when there are more than two paired sets of chromosomes), with one of the stages emphasized over the other. This is called alternation of generations The Alternation of the generations describes the life cycle of plants, fungi and protists. A multicellular diploid phase alternates with a multicellular haploid phase. The term can be confusing for people familiar only with the life cycle of a typical animal. A more understandable name would be "alternation of phases of a single generation&. Most fungi A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. The Fungi (pronounced /ˈfʌndʒaɪ/ or /ˈfʌŋɡaɪ/) are classified as a kingdom that is separate from plants, animals and bacteria. One major difference is that fungal cells have cell and algae Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms. The largest and most complex marine forms are called seaweeds. They are photosynthetic, like plants, and "simple" because they lack the many distinct organs found in land plants are haploid during the principal stage of their life cycle.
Male Male refers to the sex of an organism, or part of an organism, which produces small mobile gametes, called spermatozoa. Each spermatozoon can fuse with a larger female gamete or ovum, in the process of fertilization. A male cannot reproduce sexually without access to at least one ovum from a female, but some organisms can reproduce both sexually bees Bees are flying insects closely related to wasps and ants, and are known for their role in pollination and for producing honey and beeswax. Bees are a monophyletic lineage within the superfamily Apoidea, presently classified by the unranked taxon name Anthophila. There are nearly 20,000 known species of bees in seven to nine recognized families,, wasps The term wasp is typically defined as any insect of the order Hymenoptera and suborder Apocrita that is neither a bee nor ant. Almost every pest insect species has at least one wasp species that preys upon it or parasitizes it, making wasps critically important in natural control of their numbers, or natural biocontrol. Parasitic wasps are, and ants A phylogeny of the extant ant subfamilies are haploid organisms because of the way they develop from unfertilized, haploid egg cells An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization. In lower plants and algae, the ovum is also often called oosphere.
In humans, the monoploid number (x) equals the haploid number (n), x = n = 23, but in some species (especially plants), these numbers differ. Common wheat Bread wheat is an allohexaploid . Free-threshing wheat is closely related to spelt. As with spelt, genes contributed from goatgrass (Aegilops tauschii) give bread wheat greater cold hardiness than most wheats, and it is cultivated throughout the world's temperate regions has six sets of chromosomes in the somatic The term somatic refers to cells of the body, rather than gametes (eggs or sperm). In humans, somatic cells contain two copies of each chromosome (diploid), whereas gametes only contain one copy of each chromosome (haploid). Although all somatic cells contain identical DNA, after exposure to specific enzymes, they evolve a variety of tissue- cells, derived from its three different ancestral species. The gametes of common wheat are considered as haploid since they contain half the genetic information of somatic cells, but are not monoploid as they still contain three complete sets of chromosomes (n = 3x).
Diploid
Diploid (indicated by 2n=2x) cells have two homologous Homologous chromosomes are chromosomes in a biological cell that pair during cell division during the creation of gametes (meiosis) copies of each chromosome A chromosome is an organized structure of DNA and protein that is 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. The word chromosome comes from the Greek χρῶμα, usually one from the mother A mother is a woman who has, conceived, given birth to, or raised a child in the role of a parent. Because of the complexity and differences of a mothers' social, cultural, and religious definitions and roles, it is challenging to define a mother to suit a universally accepted definition. The masculine equivalent is a father and one from the father A father is defined as a male parent of any type of offspring. The adjective "paternal" refers to father, parallel to "maternal" for mother. The exact number of chromosomes may be one or two different from the 2 number yet the cell may still be classified as diploid (although with 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 properly between the two cells. Chromosome). Nearly all mammals are diploid organisms (the viscacha rats Pipanacoctomys aureus and Tympanoctomys barrerae are the only known exceptions as of 2004[2]), although all individuals have some small fraction of cells that display polyploidy. Human diploid cells have 46 chromosomes and human haploid gametes (egg and sperm) have 23 chromosomes.
Retroviruses A retrovirus is an RNA virus that is replicated in a host cell via the enzyme reverse transcriptase to produce DNA from its RNA genome. The DNA is then incorporated into the host's genome by an integrase enzyme. The virus thereafter replicates as part of the host cell's DNA. Retroviruses are enveloped viruses that belong to the viral family that contain two copies of their RNA genome in each viral particle are also said to be diploid. Examples include human foamy virus, human T-lymphotropic virus, and HIV Human immunodeficiency virus is a lentivirus (a member of the retrovirus family) that causes acquired immunodeficiency syndrome (AIDS), a condition in humans in which the immune system begins to fail, leading to life-threatening opportunistic infections. Infection with HIV occurs by the transfer of blood, semen, vaginal fluid, pre-ejaculate, or.[1]
Haploidisation
Haploidisation (haploidization) is the process of creating a haploid cell (usually from a diploid cell).
A laboratory procedure called haploidisation forces a normal cell to expel half of its chromosomal complement. In mammals Mammals are a class of vertebrate, air-breathing animals whose females are characterized by the possession of mammary glands while both males and females are characterized by hair and/or fur, three middle ear bones used in hearing, and a neocortex region in the brain. Some mammals have sweat glands, but most do not this renders this cell chromosomally equal to sperm or egg An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization. In lower plants and algae, the ovum is also often called oosphere. This was one of the procedures used by Japanese Japan is an island country in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south. The characters that make up Japan's name mean "sun-origin", which is why Japan is researchers to produce Kaguya, a fatherless mouse A mouse is a small mammal belonging to the order of rodents. The best known mouse species is the common house mouse (Mus musculus). It is also a popular pet. In some places, certain kinds of field mice are also common. This rodent is eaten by large birds such as hawks and eagles. They are known to invade homes for food and occasionally shelter.
Haploidisation sometimes occurs in plants when meiotically reduced cells (usually egg cells) develop by parthenogenesis Parthenogenesis is a form of asexual reproduction found in females, where growth and development of embryos occurs without fertilization by a male. In plants, parthenogenesis means development of an embryo from an unfertilized egg cell, and is a component process of apomixis. The offspring produced by parthenogenesis are always female in species.
Polyploidy
Main article: Polyploidy Polyploidy occurs in cells and organisms when there are more than two paired sets of chromosomesPolyploidy is the state where all cells have multiple sets of chromosomes beyond the basic set, for example, in triploids 2n=3x, in tetraploids 2n=4x. The chromosome sets may be from the same species or from closely related species. In the latter case these are known as allopolyploids (or amphidiploids, which are allopolyploids that behave as if they were normal diploids). Allopolyploids are formed from the hybridization of two separate species. In plants, this probably most often occurs from the pairing of meiotically unreduced gametes A gamete is a cell that fuses with another gamete during fertilization (conception) in organisms that reproduce sexually. In species that produce two morphologically distinct types of gametes, and in which each individual produces only one type, a female is any individual that produces the larger type of gamete—called an ovum (or egg)—and a, and not by diploid–diploid hybridization followed by chromosome doubling[3]. The so-called Brassica triangle is an example of allopolyploidy, where three different parent species have hybridized in each pair combination to produce three new species.
Polyploidy occurs commonly in plants, but rarely in animals. Even in diploid organisms many somatic cells are polyploid due to a process called endoreduplication where duplication of the genome occurs without mitosis (cell division).
The extreme in polyploidy occurs in the fern-ally genus Ophioglossum, the adder's-tongues, in which polyploidy results in chromosome counts in the hundreds, or in at least one case, well over one thousand. Interestingly, these plants seem to have simplified structures in their phenotype.
Variable or indefinite ploidy
Depending on growth conditions, prokaryotes such as bacteria may have a chromosome copy number of 1 to 4, and that number is commonly fractional, counting portions of the chromosome partly replicated at a given time. This is because under exponential growth conditions the cells are able to replicate their DNA faster than they can divide.
Mixoploidy
Mixoploidy refers to the presence of two cell lines, one diploid and one polyploid. Though polyploidy in humans is not viable, mixoploidy has been found in live adults and children. There are two types: diploid-triploid mixoploidy, in which some cells have 46 chromosomes and some have 69, and diploid-tetraploid mixoploidy, in which some cells have 46 and some have 92 chromosomes.
Dihaploidy and Polyhaploidy
Dihaploid and polyhaploid cells are formed by haploidisation of polyploids, i.e., by halving the chromosome constitution.
Dihaploids (which are diploid) are important for selective breeding of tetraploid crop plants (notably potatoes), because selection is faster with diploids than with tetraploids. Tetraploids can be reconstituted from the diploids, for example by somatic fusion.
The term “dihaploid” was coined by Bender[4] to combine in one word the number of genome copies (diploid) and their origin (haploid). The term is well established in this original sense[5][6], but it has also been used for doubled monoploids or doubled haploids, which are homozygous and used for genetic research[7].
References
- ^ doi:10.1126/science.231.4743.1278
- ^ Gallardo, M. H. et al. (2004). Whole-genome duplications in South American desert rodents (Octodontidae). Biological Journal of the Linnean Society, 82, 443-451.
- ^ Ramsey, J., and Schemske, D.W. 2002. "Neopolyploidy in flowering plants". Annual Review of Ecology and Systematics 33: 589–639.
- ^ Bender, K. 1963. “Über die Erzeugung und Entstehung dihaploider Pflanzen bei Solanum tuberosum”. Zeitschrift für Pflanzenzüchtung 50: 141–166.
- ^ Nogler, G.A. 1984. Gametophytic apomixis. In Embryology of angiosperms. Edited by B.M. Johri. Springer, Berlin, Germany. pp. 475–518.
- ^ * Pehu, E. 1996. The current status of knowledge on the cellular biology of potato. Potato Research 39: 429–435.
- ^ * Sprague, G.F., Russell, W.A., and Penny, L.H. 1960. Mutations affecting quantitative traits in the selfed progeny of double monoploid maize stocks. Genetics 45(7): 855–866.
- Griffiths, A. J. et al. 2000. An introduction to genetic analysis, 7th ed. W. H. Freeman, New York ISBN 0-7167-3520-2
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Categories: Classical genetics | Cytogenetics
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