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115-427: Saccharomycotina is a subdivision (subphylum) of the division (phylum) Ascomycota in the kingdom Fungi . It comprises most of the ascomycete yeasts . The members of Saccharomycotina reproduce by budding and they do not produce ascocarps (fruiting bodies). The subdivision includes a single class: Saccharomycetes , which again contains a single order: Saccharomycetales . Notable members of Saccharomycotina are

230-535: A ploidy series , featuring diploid ( X. tropicalis , 2n=20), tetraploid ( X. laevis , 4n=36), octaploid ( X. wittei , 8n=72), and dodecaploid ( X. ruwenzoriensis , 12n=108) species. Over evolutionary time scales in which chromosomal polymorphisms accumulate, these changes become less apparent by karyotype – for example, humans are generally regarded as diploid, but the 2R hypothesis has confirmed two rounds of whole genome duplication in early vertebrate ancestors. Ploidy can also vary between individuals of

345-417: A syncytium , though usually the ploidy of each nucleus is described individually. For example, a fungal dikaryon with two separate haploid nuclei is distinguished from a diploid cell in which the chromosomes share a nucleus and can be shuffled together. It is possible on rare occasions for ploidy to increase in the germline , which can result in polyploid offspring and ultimately polyploid species. This

460-1196: A thallus usually referred to as the mycelium , which—when visible to the naked eye (macroscopic)—is commonly called mold . During sexual reproduction, many Ascomycota typically produce large numbers of asci . The ascus is often contained in a multicellular, occasionally readily visible fruiting structure, the ascocarp (also called an ascoma ). Ascocarps come in a very large variety of shapes: cup-shaped, club-shaped, potato-like, spongy, seed-like, oozing and pimple-like, coral-like, nit-like, golf-ball-shaped, perforated tennis ball-like, cushion-shaped, plated and feathered in miniature ( Laboulbeniales ), microscopic classic Greek shield-shaped, stalked or sessile. They can appear solitary or clustered. Their texture can likewise be very variable, including fleshy, like charcoal (carbonaceous), leathery, rubbery, gelatinous, slimy, powdery, or cob-web-like. Ascocarps come in multiple colors such as red, orange, yellow, brown, black, or, more rarely, green or blue. Some ascomyceous fungi, such as Saccharomyces cerevisiae , grow as single-celled yeasts, which—during sexual reproduction—develop into an ascus, and do not form fruiting bodies. In lichenized species,

575-675: A zygote with n pairs of chromosomes, i.e. 2 n chromosomes in total. The chromosomes in each pair, one of which comes from the sperm and one from the egg, are said to be homologous . Cells and organisms with pairs of homologous chromosomes are called diploid. For example, most animals are diploid and produce haploid gametes. During meiosis , sex cell precursors have their number of chromosomes halved by randomly "choosing" one member of each pair of chromosomes, resulting in haploid gametes. Because homologous chromosomes usually differ genetically, gametes usually differ genetically from one another. All plants and many fungi and algae switch between

690-472: A bottle shaped cell called a phialide , from which the spores are produced. Not all of these asexual structures are a single hypha. In some groups, the conidiophores (the structures that bear the conidia) are aggregated to form a thick structure. E.g. In the order Moniliales, all of them are single hyphae with the exception of the aggregations, termed as coremia or synnema. These produce structures rather like corn-stokes, with many conidia being produced in

805-467: 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. In ciliates, the macronucleus is called ampliploid , because only part of the genome is amplified. Mixoploidy is the case where two cell lines, one diploid and one polyploid, coexist within

920-506: A double-dividing wall with a central lamella (layer) forms between the cells; the central layer then breaks down thereby releasing the spores. In rhexolytic dehiscence, the cell wall that joins the spores on the outside degenerates and releases the conidia. Several Ascomycota species are not known to have a sexual cycle. Such asexual species may be able to undergo genetic recombination between individuals by processes involving heterokaryosis and parasexual events. Parasexuality refers to

1035-433: A form of pneumonia . Asci of Ascosphaera fill honey bee larvae and pupae causing mummification with a chalk-like appearance, hence the name "chalkbrood". Yeasts for small colonies in vitro and in vivo , and excessive growth of Candida species in the mouth or vagina causes "thrush", a form of candidiasis . The cell walls of the ascomycetes almost always contain chitin and β-glucans , and divisions within

1150-476: A further mitotic division that results in eight nuclei in each ascus. The nuclei along with some cytoplasma become enclosed within membranes and a cell wall to give rise to ascospores that are aligned inside the ascus like peas in a pod. Upon opening of the ascus, ascospores may be dispersed by the wind, while in some cases the spores are forcibly ejected form the ascus; certain species have evolved spore cannons, which can eject ascospores up to 30 cm. away. When

1265-424: A germ cell with an uneven number of chromosomes undergoes meiosis, the chromosomes cannot be evenly divided between the daughter cells, resulting in aneuploid gametes. Triploid organisms, for instance, are usually sterile. Because of this, triploidy is commonly exploited in agriculture to produce seedless fruit such as bananas and watermelons. If the fertilization of human gametes results in three sets of chromosomes,

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1380-629: A haploid and a diploid state, with one of the stages emphasized over the other. This is called alternation of generations . Most fungi and algae are haploid during the principal stage of their life cycle, as are some primitive plants like mosses . More recently evolved plants, like the gymnosperms and angiosperms , spend the majority of their life cycle in the diploid stage. Most animals are diploid, but male bees , wasps , and ants are haploid organisms because they develop from unfertilized, haploid eggs, while females (workers and queens) are diploid, making their system haplodiploid . In some cases there

1495-737: A hypha. Vegetative hyphae of most ascomycetes contain only one nucleus per cell ( uninucleate hyphae), but multinucleate cells—especially in the apical regions of growing hyphae—can also be present. In common with other fungal phyla, the Ascomycota are heterotrophic organisms that require organic compounds as energy sources. These are obtained by feeding on a variety of organic substrates including dead matter, foodstuffs, or as symbionts in or on other living organisms. To obtain these nutrients from their surroundings, ascomycetous fungi secrete powerful digestive enzymes that break down organic substances into smaller molecules, which are then taken up into

1610-529: A large-scale specialized structure that helps to spread them. These two basic types can be further classified as follows: Sometimes the conidia are produced in structures visible to the naked eye, which help to distribute the spores. These structures are called "conidiomata" (singular: conidioma ), and may take the form of pycnidia (which are flask-shaped and arise in the fungal tissue) or acervuli (which are cushion-shaped and arise in host tissue). Dehiscence happens in two ways. In schizolytic dehiscence,

1725-433: A mass from the aggregated conidiophores. The diverse conidia and conidiophores sometimes develop in asexual sporocarps with different characteristics (e.g. acervulus, pycnidium, sporodochium). Some species of ascomycetes form their structures within plant tissue, either as parasite or saprophytes. These fungi have evolved more complex asexual sporing structures, probably influenced by the cultural conditions of plant tissue as

1840-451: A number of chromosomes that is an exact multiple of the number of chromosomes in a normal gamete; and having any other number, respectively. For example, a person with Turner syndrome may be missing one sex chromosome (X or Y), resulting in a (45,X) karyotype instead of the usual (46,XX) or (46,XY). This is a type of aneuploidy and cells from the person may be said to be aneuploid with a (diploid) chromosome complement of 45. The term ploidy

1955-425: A process called endoreduplication , where duplication of the genome occurs without mitosis (cell division). The extreme in polyploidy occurs in the fern 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. It is possible for polyploid organisms to revert to lower ploidy by haploidisation . Polyploidy

2070-545: A separate artificial phylum , the Deuteromycota (or "Fungi Imperfecti"). Where recent molecular analyses have identified close relationships with ascus-bearing taxa, anamorphic species have been grouped into the Ascomycota, despite the absence of the defining ascus. Sexual and asexual isolates of the same species commonly carry different binomial species names, as, for example, Aspergillus nidulans and Emericella nidulans , for asexual and sexual isolates, respectively, of

2185-401: A single nucleus rather than in the cell as a whole. Because in most situations there is only one nucleus per cell, it is commonplace to speak of the ploidy of a cell, but in cases in which there is more than one nucleus per cell, more specific definitions are required when ploidy is discussed. Authors may at times report the total combined ploidy of all nuclei present within the cell membrane of

2300-437: A single chromosome and diploid individuals have two chromosomes. In Entamoeba , the ploidy level varies from 4 n to 40 n in a single population. Alternation of generations occurs in most plants, with individuals "alternating" ploidy level between different stages of their sexual life cycle. In large multicellular organisms, variations in ploidy level between different tissues, organs, or cell lineages are common. Because

2415-495: A single copy of each chromosome – that is, one and only one set of chromosomes. In this case, the nucleus of a eukaryotic cell is said to be haploid only if it has a single set of chromosomes , each one not being part of a pair. By extension a cell may be called haploid if its nucleus has one set of chromosomes, and an organism may be called haploid if its body cells (somatic cells) have one set of chromosomes per cell. By this definition haploid therefore would not be used to refer to

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2530-484: A single parent, without the involvement of gametes and fertilization, and all the offspring are genetically identical to each other and to the parent, including in chromosome number. The parents of these vegetative clones may still be capable of producing haploid gametes in preparation for sexual reproduction, but these gametes are not used to create the vegetative offspring by this route. Some eukaryotic genome-scale or genome size databases and other sources which may list

2645-408: A substrate. These structures are called the sporodochium . This is a cushion of conidiophores created from a pseudoparenchymatous stroma in plant tissue. The pycnidium is a globose to flask-shaped parenchymatous structure, lined on its inner wall with conidiophores. The acervulus is a flat saucer shaped bed of conidiophores produced under a plant cuticle, which eventually erupt through

2760-551: A tetraploid nucleus which divided into four diploid nuclei by meiosis and then into eight haploid nuclei by a supposed process called brachymeiosis , but this hypothesis was disproven in the 1950s. From the fertilized ascogonium, dinucleate hyphae emerge in which each cell contains two nuclei. These hyphae are called ascogenous or fertile hyphae. They are supported by the vegetative mycelium containing uni– (or mono–) nucleate hyphae, which are sterile. The mycelium containing both sterile and fertile hyphae may grow into fruiting body,

2875-423: A variety of stresses such as nutrient limitation. The sexual part of the life cycle commences when two hyphal structures mate . In the case of homothallic species, mating is enabled between hyphae of the same fungal clone , whereas in heterothallic species, the two hyphae must originate from fungal clones that differ genetically, i.e., those that are of a different mating type . Mating types are typical of

2990-490: Is 24. The monoploid number equals the total chromosome number divided by the ploidy level of the somatic cells: 48 chromosomes in total divided by a ploidy level of 4 equals a monoploid number of 12. Hence, the monoploid number (12) and haploid number (24) are distinct in this example. However, commercial potato crops (as well as many other crop plants) are commonly propagated vegetatively (by asexual reproduction through mitosis), in which case new individuals are produced from

3105-402: Is 7. The gametes of common wheat are considered to be haploid, since they contain half the genetic information of somatic cells, but they are not monoploid, as they still contain three complete sets of chromosomes ( n  = 3 x ). In the case of wheat, the origin of its haploid number of 21 chromosomes from three sets of 7 chromosomes can be demonstrated. In many other organisms, although

3220-515: Is a back-formation from haploidy and diploidy . "Ploid" is a combination of Ancient Greek -πλόος (-plóos, "-fold") and -ειδής (- eidḗs ), from εἶδος ( eîdos , "form, likeness"). The principal meaning of the Greek word ᾰ̔πλόος (haplóos) is "single", from ἁ- (ha-, "one, same"). διπλόος ( diplóos ) means "duplex" or "two-fold". Diploid therefore means "duplex-shaped" (compare "humanoid", "human-shaped"). Polish-German botanist Eduard Strasburger coined

3335-417: Is a dictyospore . In staurospores ray-like arms radiate from a central body; in others ( helicospores ) the entire spore is wound up in a spiral like a spring. Very long worm-like spores with a length-to-diameter ratio of more than 15:1, are called scolecospores . Important characteristics of the anamorphs of the Ascomycota are conidiogenesis , which includes spore formation and dehiscence (separation from

3450-779: Is a phylum of the kingdom Fungi that, together with the Basidiomycota , forms the subkingdom Dikarya . Its members are commonly known as the sac fungi or ascomycetes . It is the largest phylum of Fungi, with over 64,000 species . The defining feature of this fungal group is the " ascus " (from Ancient Greek ἀσκός ( askós )  'sac, wineskin'), a microscopic sexual structure in which nonmotile spores , called ascospores , are formed. However, some species of Ascomycota are asexual and thus do not form asci or ascospores. Familiar examples of sac fungi include morels , truffles , brewers' and bakers' yeast , dead man's fingers , and cup fungi . The fungal symbionts in

3565-430: Is a sister group to Pezizomycotina . Yeasts were traditionally classified as a separate group of the fungal kingdom, but in recent years DNA-based methods have changed the understanding of phylogenetic relationships among fungi. Yeasts are considered to be a polyphyletic group, consisting of members of Basidiomycota , Taphrinomycotina , as well as Saccharomycotina. This realization has led to major changes in

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3680-413: Is a characteristic of the bacterium Deinococcus radiodurans and of the archaeon Halobacterium salinarum . These two species are highly resistant to ionizing radiation and desiccation , conditions that induce DNA double-strand breaks. This resistance appears to be due to efficient homologous recombinational repair. Depending on growth conditions, prokaryotes such as bacteria may have

3795-484: Is a tube-shaped vessel, a meiosporangium , which contains the sexual spores produced by meiosis and which are called ascospores . Apart from a few exceptions, such as Candida albicans , most ascomycetes are haploid , i.e., they contain one set of chromosomes per nucleus. During sexual reproduction there is a diploid phase, which commonly is very short, and meiosis restores the haploid state. The sexual cycle of one well-studied representative species of Ascomycota

3910-1275: Is an example of a genus that is undergoing large-scale revisions. Molecular identification methods are important tools for discovery of new species and subsequently give better understanding of biodiversity in this group. Much of the future classification of Saccharomycotina will rest on phylogenetic analysis of DNA sequences rather than on the morphological and developmental characters. Phylogeny by Groenewald et al. 2023 Lipomycetaceae Novák & Zsolt 1961 Trigonopsidaceae Lachance & Kurtzman 2013 Dipodascaceae Trichomonascaceae Alloascoideaceae Kurtzman & Robnett 2013 Sporopachydermiaceae Groenewald et al. 2023 Pachysolenaceae Groenewald et al. 2023 Pichiaceae Zender 1925 Cephaloascaceae Batra 1973 Metschnikowiaceae Kamienski 1899 ex Doweld 2013 Debaryomycetaceae Kurtzman & Suzuki 2010 Ascoideaceae Engl. 1892 Saccharomycopsidaceae Arx & Van der Walt 1987 Wickerhamomycetaceae Kurtzman, Robnett & Bas.-Powers 2008 Phaffomycetaceae Yamada et al. 1999 Saccharomycodaceae Kudrjanzev 1960 Endomycetaceae Schröter 1893 Saccharomycetaceae Winter 1881 Ascomycota Ascomycota

4025-412: Is an important evolutionary mechanism in both plants and animals and is known as a primary driver of speciation . As a result, it may become desirable to distinguish between the ploidy of a species or variety as it presently breeds and that of an ancestor. The number of chromosomes in the ancestral (non-homologous) set is called the monoploid number ( x ), and is distinct from the haploid number ( n ) in

4140-462: Is associated with a 14% lower risk of being endangered, and a 20% greater chance of being invasive. Polyploidy may be associated with increased vigor and adaptability. Some studies suggest that selection is more likely to favor diploidy in host species and haploidy in parasite species. However, polyploidization is associated with an increase in transposable element content and relaxed purifying selection on recessive deleterious alleles. When

4255-652: Is characterized by holoblastic budding, which means all layers of the parent cell wall are involved in the budding event. This leaves a scar through which no further budding occurs. Asexual cells may vary in shape. The shape of the cell may be informative in terms of detecting mode of reproduction or taxonomic placement to genera or species. Although not commonly known, some species form endospores (e.g. Candida species). These are asexual spores that are formed within their mother cell (hyphal or single cell). Strains of Candida and Metschnikowia may also form asexual resting spores called chlamydospores . Sexual reproduction

4370-451: Is described in greater detail in Neurospora crassa . Also, the adaptive basis for the maintenance of sexual reproduction in the Ascomycota fungi was reviewed by Wallen and Perlin. They concluded that the most plausible reason for the maintenance of this capability is the benefit of repairing DNA damage by using recombination that occurs during meiosis . DNA damage can be caused by

4485-525: Is evidence that the n chromosomes in a haploid set have resulted from duplications of an originally smaller set of chromosomes. This "base" number – the number of apparently originally unique chromosomes in a haploid set – is called the monoploid number , also known as basic or cardinal number , or fundamental number . As an example, the chromosomes of common wheat are believed to be derived from three different ancestral species, each of which had 7 chromosomes in its haploid gametes. The monoploid number

4600-672: Is fairly simple, although their growth form is highly adapted. Asci are naked and ascospores can have several forms. No species produce ascocarps (fruiting bodies). Saccharomycete genomes are often smaller than those of filamentous fungi . Some species (e.g. Metschnikowia species) tend to form chains of budding cells that are termed pseudohyphae . Yet other species are able to produce true septate hyphae . Such species (e.g. Candida albicans ) are termed dimorphic , which means they can propagate both as budding yeasts and as filamentous hyphae. Asexual reproduction occurs mainly vegetatively by mitosis and budding . Saccharomycotina

4715-468: Is faster than diploid under high nutrient conditions. The NLH is also tested in haploid, diploid, and polyploid fungi by Gerstein et al. 2017. This result is also more complex: On the one hand, under phosphorus and other nutrient limitation, lower ploidy is selected as expected. However under normal nutrient levels or under limitation of only nitrogen , higher ploidy was selected. Thus the NLH – and more generally,

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4830-414: Is important for understanding yeast ecology , something that is now possible with the increased use of DNA-based methods . Before molecular methods were available, identification was mainly based on morphology , something that resulted in misclassifications and further prevented reliable results of ecological research. Saccharomycotina is a subdivision (subphylum) of the division (phylum) Ascomycota . It

4945-461: Is not known for all species of Saccharomycotina, but may happen in certain species if environmental conditions favour it (e.g. deficiency in nitrogen and carbohydrate ). Sexual reproduction is well known in Saccharomyces cerevisiae . Here, the life cycle involves alternation between a haploid and a diploid phase. The life cycle proceeds as follows: Two cells of different mating type fuse and

5060-522: Is only found on Nothofagus (Southern Beech) in the Southern Hemisphere . Asexual reproduction is the dominant form of propagation in the Ascomycota, and is responsible for the rapid spread of these fungi into new areas. It occurs through vegetative reproductive spores, the conidia . The conidiospores commonly contain one nucleus and are products of mitotic cell divisions and thus are sometimes called mitospores, which are genetically identical to

5175-572: Is the simplest to illustrate in diagrams of genetics concepts. But this definition also allows for haploid gametes with more than one set of chromosomes. As given above, gametes are by definition haploid, regardless of the actual number of sets of chromosomes they contain. An organism whose somatic cells are tetraploid (four sets of chromosomes), for example, will produce gametes by meiosis that contain two sets of chromosomes. These gametes might still be called haploid even though they are numerically diploid. An alternative usage defines "haploid" as having

5290-426: Is the state in which the chromosomes are paired and can undergo meiosis. The zygoid state of a species may be diploid or polyploid. In the azygoid state the chromosomes are unpaired. It may be the natural state of some asexual species or may occur after meiosis. In diploid organisms the azygoid state is monoploid. (See below for dihaploidy.) In the strictest sense, ploidy refers to the number of sets of chromosomes in

5405-731: Is the state where all cells have multiple sets of chromosomes beyond the basic set, usually 3 or more. Specific terms are triploid (3 sets), tetraploid (4 sets), pentaploid (5 sets), hexaploid (6 sets), heptaploid or septaploid (7 sets), octoploid (8 sets), nonaploid (9 sets), decaploid (10 sets), undecaploid (11 sets), dodecaploid (12 sets), tridecaploid (13 sets), tetradecaploid (14 sets), etc. Some higher ploidies include hexadecaploid (16 sets), dotriacontaploid (32 sets), and tetrahexacontaploid (64 sets), though Greek terminology may be set aside for readability in cases of higher ploidy (such as "16-ploid"). Polytene chromosomes of plants and fruit flies can be 1024-ploid. Ploidy of systems such as

5520-402: Is thus 7 and the haploid number is 3 × 7 = 21. In general n is a multiple of x . The somatic cells in a wheat plant have six sets of 7 chromosomes: three sets from the egg and three sets from the sperm which fused to form the plant, giving a total of 42 chromosomes. As a formula, for wheat 2 n  = 6 x  = 42, so that the haploid number n is 21 and the monoploid number x

5635-463: Is usually inconspicuous because it is commonly embedded in the substrate, such as soil, or grows on or inside a living host, and only the ascoma may be seen when fruiting. Pigmentation , such as melanin in hyphal walls, along with prolific growth on surfaces can result in visible mold colonies; examples include Cladosporium species, which form black spots on bathroom caulking and other moist areas. Many ascomycetes cause food spoilage, and, therefore,

5750-417: Is well established in this original sense, but it has also been used for doubled monoploids or doubled haploids , which are homozygous and used for genetic research. Euploidy ( Greek eu , "true" or "even") is the state of a cell or organism having one or more than one set of the same set of chromosomes, possibly excluding the sex-determining chromosomes . For example, most human cells have 2 of each of

5865-416: The ascocarp , which may contain millions of fertile hyphae. An ascocarp is the fruiting body of the sexual phase in Ascomycota. There are five morphologically different types of ascocarp, namely: The sexual structures are formed in the fruiting layer of the ascocarp, the hymenium . At one end of ascogenous hyphae, characteristic U-shaped hooks develop, which curve back opposite to the growth direction of

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5980-402: The ascogonium , and merges with a gametangium (the antheridium ) of the other fungal isolate. The nuclei in the antheridium then migrate into the ascogonium, and plasmogamy —the mixing of the cytoplasm —occurs. Unlike in animals and plants, plasmogamy is not immediately followed by the merging of the nuclei (called karyogamy ). Instead, the nuclei from the two hyphae form pairs, initiating

6095-452: The conidia . The asexual, non-motile haploid spores of a fungus, which are named after the Greek word for dust (conia), are hence also known as conidiospores . The conidiospores commonly contain one nucleus and are products of mitotic cell divisions and thus are sometimes called mitospores , which are genetically identical to the mycelium from which they originate. They are typically formed at

6210-627: The detritivores (animals that feed on decomposing material) to obtain their nutrients. Ascomycetes, along with other fungi, can break down large molecules such as cellulose or lignin , and thus have important roles in nutrient cycling such as the carbon cycle . The fruiting bodies of the Ascomycota provide food for many animals ranging from insects and slugs and snails ( Gastropoda ) to rodents and larger mammals such as deer and wild boars . Many ascomycetes also form symbiotic relationships with other organisms, including plants and animals. Probably since early in their evolutionary history,

6325-401: The dikaryophase of the sexual cycle, during which time the pairs of nuclei synchronously divide. Fusion of the paired nuclei leads to mixing of the genetic material and recombination and is followed by meiosis . A similar sexual cycle is present in the red algae (Rhodophyta). A discarded hypothesis held that a second karyogamy event occurred in the ascogonium prior to ascogeny, resulting in

6440-685: The ergot fungi, black knot , and the powdery mildews . The members of the genus Cordyceps are entomopathogenic fungi , meaning that they parasitise and kill insects. Other entomopathogenic ascomycetes have been used successfully in biological pest control , such as Beauveria . Several species of ascomycetes are biological model organisms in laboratory research. Most famously, Neurospora crassa , several species of yeasts , and Aspergillus species are used in many genetics and cell biology studies. Ascomycetes are 'spore shooters'. They are fungi which produce microscopic spores inside special, elongated cells or sacs, known as 'asci', which give

6555-423: The monoploid number ( x ). The haploid number ( n ) refers to the total number of chromosomes found in a gamete (a sperm or egg cell produced by meiosis in preparation for sexual reproduction). Under normal conditions, the haploid number is exactly half the total number of chromosomes present in the organism's somatic cells, with one paternal and maternal copy in each chromosome pair. For diploid organisms,

6670-541: The photoautotrophic algal partner generates metabolic energy through photosynthesis, the fungus offers a stable, supportive matrix and protects cells from radiation and dehydration. Around 42% of the Ascomycota (about 18,000 species) form lichens, and almost all the fungal partners of lichens belong to the Ascomycota. Diploid Virtually all sexually reproducing organisms are made up of somatic cells that are diploid or greater, but ploidy level may vary widely between different organisms, between different tissues within

6785-667: The phylogeny and taxonomy of Saccharomycotina. In addition, the recent changes in the International Code of Nomenclature for algae, fungi and plants have had a major impact on the classification of fungi, including Saccharomycotina. The changes imply that a fungus can only bear one correct name, i.e. separate names for anamorphs and teleomorphs are no longer allowed. This involves major changes in Saccharomycotina taxonomy , as many species are currently described from both anamorphic and teleomorphic stages. The genus Candida

6900-425: The salivary gland , elaiosome , endosperm , and trophoblast can exceed this, up to 1048576-ploid in the silk glands of the commercial silkworm Bombyx mori . 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

7015-453: The 23 homologous monoploid chromosomes, for a total of 46 chromosomes. A human cell with one extra set of the 23 normal chromosomes (functionally triploid) would be considered euploid. Euploid karyotypes would consequentially be a multiple of the haploid number , which in humans is 23. Aneuploidy is the state where one or more individual chromosomes of a normal set are absent or present in more than their usual number of copies (excluding

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7130-407: The 23 homologous pairs of chromosomes that humans normally have. This results in two homologous pairs within each of the 23 homologous pairs, providing a full complement of 46 chromosomes. This total number of individual chromosomes (counting all complete sets) is called the chromosome number or chromosome complement . The number of chromosomes found in a single complete set of chromosomes is called

7245-533: The Ascomycota have formed symbiotic associations with green algae ( Chlorophyta ), and other types of algae and cyanobacteria . These mutualistic associations are commonly known as lichens , and can grow and persist in terrestrial regions of the earth that are inhospitable to other organisms and characterized by extremes in temperature and humidity, including the Arctic , the Antarctic , deserts , and mountaintops. While

7360-410: The Ascomycota. The most frequent types are the single-celled spores, which are designated amerospores . If the spore is divided into two by a cross-wall ( septum ), it is called a didymospore . When there are two or more cross-walls, the classification depends on spore shape. If the septae are transversal , like the rungs of a ladder, it is a phragmospore , and if they possess a net-like structure it

7475-629: The Ascomycota. These include the following sexual ( teleomorphic ) groups, defined by the structures of their sexual fruiting bodies : the Discomycetes , which included all species forming apothecia ; the Pyrenomycetes , which included all sac fungi that formed perithecia or pseudothecia , or any structure resembling these morphological structures; and the Plectomycetes, which included those species that form cleistothecia . Hemiascomycetes included

7590-564: The absence or presence of complete sets, which is considered euploidy). Unlike euploidy, aneuploid karyotypes will not be a multiple of the haploid number. In humans, examples of aneuploidy include having a single extra chromosome (as in Down syndrome , where affected individuals have three copies of chromosome 21) or missing a chromosome (as in Turner syndrome , where affected individuals have only one sex chromosome). Aneuploid karyotypes are given names with

7705-449: The atmosphere and freshwater environments, as well as ocean beaches and tidal zones. The distribution of species is variable; while some are found on all continents, others, as for example the white truffle Tuber magnatum , only occur in isolated locations in Italy and Eastern Europe. The distribution of plant-parasitic species is often restricted by host distributions; for example, Cyttaria

7820-520: The atmosphere. Their growth is mainly saprotrophic , but some members are important pathogens of plants and animals, including humans. They are often found in specialized habitats, e.g. small volumes of organic carbon rich liquid (e.g. flower nectar). Examples of ecological modes in Saccharomycotina: Although yeasts are commonly isolated from soil, few are believed to have soil as a primary habitat . Accurate identification of species

7935-434: The baker's yeast Saccharomyces cerevisiae and the genus Candida that includes several human pathogens. The name comes from the Greek word σάκχαρον ( sákkharon ), meaning "sugar" and μύκης ( mukēs ) meaning "fungus". Historical records from ancient Egypt and China describe the processes of brewing and baking from 10,000 to 8,000 years ago, and the production of fermented beverages and foods seems to have paralleled

8050-712: The beginning of agriculture . In the 1850s, Louis Pasteur demonstrated that yeasts are responsible for the fermentation of grape juice to wine. Saccharomycotina include some of the economically most important fungi known. Members include species of industrial and agricultural importance (e.g. brewing , baking , fermentation of food products, production of citric acid , production of recombinant proteins , biofuel production, biological pest control of crops). Other species cause economic losses worldwide ( plant pathogens , contaminants of foods and beverages). Yet others are animal and human pathogens . Saccharomycete yeasts usually grow as single cells. Their cellular morphology

8165-755: The cell. Many species live on dead plant material such as leaves, twigs, or logs. Several species colonize plants, animals, or other fungi as parasites or mutualistic symbionts and derive all their metabolic energy in form of nutrients from the tissues of their hosts. Owing to their long evolutionary history, the Ascomycota have evolved the capacity to break down almost every organic substance. Unlike most organisms, they are able to use their own enzymes to digest plant biopolymers such as cellulose or lignin . Collagen , an abundant structural protein in animals, and keratin —a protein that forms hair and nails—, can also serve as food sources. Unusual examples include Aureobasidium pullulans , which feeds on wall paint, and

8280-437: 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 to combine in one word the number of genome copies (diploid) and their origin (haploid). The term

8395-453: The chromosome number is generally reduced only by the specialized process of meiosis, the somatic cells of the body inherit and maintain the chromosome number of the zygote by mitosis. However, in many situations somatic cells double their copy number by means of endoreduplication as an aspect of cellular differentiation . For example, the hearts of two-year-old human children contain 85% diploid and 15% tetraploid nuclei, but by 12 years of age

8510-499: The condition is called triploid syndrome . In unicellular organisms the ploidy nutrient limitation hypothesis suggests that nutrient limitation should encourage haploidy in preference to higher ploidies. This hypothesis is due to the higher surface-to-volume ratio of haploids, which eases nutrient uptake, thereby increasing the internal nutrient-to-demand ratio. Mable 2001 finds Saccharomyces cerevisiae to be somewhat inconsistent with this hypothesis however, as haploid growth

8625-417: The cuticle for dispersal. Asexual reproduction process in ascomycetes also involves the budding which we clearly observe in yeast. This is termed a "blastic process". It involves the blowing out or blebbing of the hyphal tip wall. The blastic process can involve all wall layers, or there can be a new cell wall synthesized which is extruded from within the old wall. The initial events of budding can be seen as

8740-605: The development of a ring of chitin around the point where the bud is about to appear. This reinforces and stabilizes the cell wall. Enzymatic activity and turgor pressure act to weaken and extrude the cell wall. New cell wall material is incorporated during this phase. Cell contents are forced into the progeny cell, and as the final phase of mitosis ends a cell plate, the point at which a new cell wall will grow inwards from, forms. There are three subphyla that are described and accepted: Several outdated taxon names—based on morphological features—are still occasionally used for species of

8855-423: The diploid stage are under less efficient natural selection than those genes expressed in the haploid stage is referred to as the “masking theory”. Evidence in support of this masking theory has been reported in studies of the single-celled yeast Saccharomyces cerevisiae . In further support of the masking theory, evidence of strong purifying selection in haploid tissue-specific genes has been reported for

8970-407: The ends of specialized hyphae, the conidiophores. Depending on the species they may be dispersed by wind or water, or by animals. Conidiophores may simply branch off from the mycelia or they may be formed in fruiting bodies. The hypha that creates the sporing (conidiating) tip can be very similar to the normal hyphal tip, or it can be differentiated. The most common differentiation is the formation of

9085-663: The fungal symbiont directly obtains products of photosynthesis . In common with many basidiomycetes and Glomeromycota , some ascomycetes form symbioses with plants by colonizing the roots to form mycorrhizal associations. The Ascomycota also represents several carnivorous fungi , which have developed hyphal traps to capture small protists such as amoebae , as well as roundworms ( Nematoda ), rotifers , tardigrades , and small arthropods such as springtails ( Collembola ). The Ascomycota are represented in all land ecosystems worldwide, occurring on all continents including Antarctica . Spores and hyphal fragments are dispersed through

9200-428: The fungi and correspond roughly to the sexes in plants and animals; however one species may have more than two mating types, resulting in sometimes complex vegetative incompatibility systems. The adaptive function of mating type is discussed in Neurospora crassa . Gametangia are sexual structures formed from hyphae, and are the generative cells. A very fine hypha, called trichogyne emerges from one gametangium,

9315-425: The gametes produced by the tetraploid organism in the example above, since these gametes are numerically diploid. The term monoploid is often used as a less ambiguous way to describe a single set of chromosomes; by this second definition, haploid and monoploid are identical and can be used interchangeably. Gametes ( sperm and ova ) are haploid cells. The haploid gametes produced by most organisms combine to form

9430-517: The group its name. Asexual reproduction is the dominant form of propagation in the Ascomycota, and is responsible for the rapid spread of these fungi into new areas. Asexual reproduction of ascomycetes is very diverse from both structural and functional points of view. The most important and general is production of conidia, but chlamydospores are also frequently produced. Furthermore, Ascomycota also reproduce asexually through budding. Asexual reproduction may occur through vegetative reproductive spores,

9545-419: The haploid number n  = 21). The gametes are haploid for their own species, but triploid, with three sets of chromosomes, by comparison to a probable evolutionary ancestor, einkorn wheat . Tetraploidy (four sets of chromosomes, 2 n  = 4 x ) is common in many plant species, and also occurs in amphibians , reptiles , and insects . For example, species of Xenopus (African toads) form

9660-518: The hook with one nucleus, one at the basal of the original hypha that contains one nucleus, and one that separates the U-shaped part, which contains the other two nuclei. Fusion of the nuclei (karyogamy) takes place in the U-shaped cells in the hymenium, and results in the formation of a diploid zygote . The zygote grows into the ascus , an elongated tube-shaped or cylinder-shaped capsule. Meiosis then gives rise to four haploid nuclei, usually followed by

9775-532: The hybridization of two separate species. In plants, this probably most often occurs from the pairing of meiotically unreduced gametes , and not by diploid–diploid hybridization followed by chromosome doubling. The so-called Brassica triangle is an example of allopolyploidy, where three different parent species have hybridized in all possible pair combinations 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

9890-446: The hyphae, called " septa ", are the internal boundaries of individual cells (or compartments). The cell wall and septa give stability and rigidity to the hyphae and may prevent loss of cytoplasm in case of local damage to cell wall and cell membrane . The septa commonly have a small opening in the center, which functions as a cytoplasmic connection between adjacent cells, also sometimes allowing cell-to-cell movement of nuclei within

10005-416: The hyphae. The two nuclei contained in the apical part of each hypha divide in such a way that the threads of their mitotic spindles run parallel, creating two pairs of genetically different nuclei. One daughter nucleus migrates close to the hook, while the other daughter nucleus locates to the basal part of the hypha. The formation of two parallel cross-walls then divides the hypha into three sections: one at

10120-579: The idea that haploidy is selected by harsher conditions – is cast into doubt by these results. Older WGDs have also been investigated. Only as recently as 2015 was the ancient whole genome duplication in Baker's yeast proven to be allopolyploid , by Marcet-Houben and Gabaldón 2015. It still remains to be explained why there are not more polyploid events in fungi, and the place of neopolyploidy and mesopolyploidy in fungal history . The concept that those genes of an organism that are expressed exclusively in

10235-612: The kerosene fungus Amorphotheca resinae , which feeds on aircraft fuel (causing occasional problems for the airline industry), and may sometimes block fuel pipes. Other species can resist high osmotic stress and grow, for example, on salted fish, and a few ascomycetes are aquatic. The Ascomycota is characterized by a high degree of specialization; for instance, certain species of Laboulbeniales attack only one particular leg of one particular insect species. Many Ascomycota engage in symbiotic relationships such as in lichens—symbiotic associations with green algae or cyanobacteria —in which

10350-1159: The majority of lichens (loosely termed "ascolichens") such as Cladonia belong to the Ascomycota. Ascomycota is a monophyletic group (containing all of the descendants of a common ancestor). Previously placed in the Basidiomycota along with asexual species from other fungal taxa, asexual (or anamorphic ) ascomycetes are now identified and classified based on morphological or physiological similarities to ascus-bearing taxa , and by phylogenetic analyses of DNA sequences. Ascomycetes are of particular use to humans as sources of medicinally important compounds such as antibiotics , as well as for fermenting bread, alcoholic beverages, and cheese. Examples of ascomycetes include Penicillium species on cheeses and those producing antibiotics for treating bacterial infectious diseases . Many ascomycetes are pathogens , both of animals, including humans, and of plants. Examples of ascomycetes that can cause infections in humans include Candida albicans , Aspergillus niger and several tens of species that cause skin infections . The many plant-pathogenic ascomycetes include apple scab , rice blast ,

10465-404: The mating. The pheromones do not affect the same mating type or diploids , but bind to receptors of different mating type. Interaction between pheromone and receptor results in altered metabolism to allow for fusion between cells of different mating type. Saccharomycete yeasts are found in nearly all regions of the world, including hot deserts, polar areas, in freshwater, in salt water, and in

10580-455: The monoploid number and haploid number are equal; in humans, both are equal to 23. When a human germ cell undergoes meiosis, the diploid 46 chromosome complement is split in half to form haploid gametes. After fusion of a male and a female gamete (each containing 1 set of 23 chromosomes) during fertilization , the resulting zygote again has the full complement of 46 chromosomes: 2 sets of 23 chromosomes. Euploidy and aneuploidy describe having

10695-418: The most generic sense, haploid refers to having the number of sets of chromosomes normally found in a gamete . Because two gametes necessarily combine during sexual reproduction to form a single zygote from which somatic cells are generated, healthy gametes always possess exactly half the number of sets of chromosomes found in the somatic cells, and therefore "haploid" in this sense refers to having exactly half

10810-402: The mycelium from which they originate. They are typically formed at the ends of specialized hyphae , the conidiophores . Depending on the species they may be dispersed by wind or water, or by animals. Different types of asexual spores can be identified by colour, shape, and how they are released as individual spores. Spore types can be used as taxonomic characters in the classification within

10925-702: The nuclei undergo karyogamy . This results in a daughter cell with a diploid nucleus, functioning as an ascus , where meiosis occurs to produce haploid ascospores . When ascospores germinate, the haploid phase is established, and is maintained by further mitosis and budding . In most natural populations this phase is fairly short since ascospores fuse almost immediately after meiosis has occurred. This results in most yeast populations being diploid for most part of their life cycle. In Saccharomycotina there are two mating types present. The mating types specify peptide hormones called pheromones and corresponding receptors for each type. These pheromones organize

11040-565: The number of chromosomes may have originated in this way, this is no longer clear, and the monoploid number is regarded as the same as the haploid number. Thus in humans, x  =  n  = 23. Diploid cells have two homologous copies of each chromosome , usually one from the mother and one from the father . All or nearly all mammals are diploid organisms. The suspected tetraploid (possessing four-chromosome sets) plains viscacha rat ( Tympanoctomys barrerae ) and golden viscacha rat ( Pipanacoctomys aureus ) have been regarded as

11155-406: The number of sets of chromosomes found in a somatic cell. By this definition, an organism whose gametic cells contain a single copy of each chromosome (one set of chromosomes) may be considered haploid while the somatic cells, containing two copies of each chromosome (two sets of chromosomes), are diploid. This scheme of diploid somatic cells and haploid gametes is widely used in the animal kingdom and

11270-694: The only known exceptions (as of 2004). However, some genetic studies have rejected any polyploidism in mammals as unlikely, and suggest that amplification and dispersion of repetitive sequences best explain the large genome size of these two rodents. All normal diploid individuals have some small fraction of cells that display polyploidy . Human diploid cells have 46 chromosomes (the somatic number, 2n ) and human haploid gametes (egg and sperm) have 23 chromosomes ( n ). Retroviruses 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 . Polyploidy

11385-409: The organism as it now reproduces. Common wheat ( Triticum aestivum ) is an organism in which x and n differ. Each plant has a total of six sets of chromosomes (with two sets likely having been obtained from each of three different diploid species that are its distant ancestors). The somatic cells are hexaploid, 2 n  = 6 x  = 42 (where the monoploid number x  = 7 and

11500-436: The original parent nuclei. Alternatively, nuclei may lose some chromosomes, resulting in aneuploid cells. Candida albicans (class Saccharomycetes) is an example of a fungus that has a parasexual cycle (see Candida albicans and Parasexual cycle ). Sexual reproduction in the Ascomycota leads to the formation of the ascus , the structure that defines this fungal group and distinguishes it from other fungal phyla. The ascus

11615-413: The parent structure). Conidiogenesis corresponds to Embryology in animals and plants and can be divided into two fundamental forms of development: blastic conidiogenesis, where the spore is already evident before it separates from the conidiogenic hypha, and thallic conidiogenesis, during which a cross-wall forms and the newly created cell develops into a spore. The spores may or may not be generated in

11730-472: The pellicles or moldy layers that develop on jams, juices, and other foods are the mycelia of these species or occasionally Mucoromycotina and almost never Basidiomycota . Sooty molds that develop on plants, especially in the tropics are the thalli of many species. Large masses of yeast cells, asci or ascus-like cells, or conidia can also form macroscopic structures. For example. Pneumocystis species can colonize lung cavities (visible in x-rays), causing

11845-403: The plant Scots Pine . The common potato ( Solanum tuberosum ) is an example of a tetraploid organism, carrying four sets of chromosomes. During sexual reproduction, each potato plant inherits two sets of 12 chromosomes from the pollen parent, and two sets of 12 chromosomes from the ovule parent. The four sets combined provide a full complement of 48 chromosomes. The haploid number (half of 48)

11960-656: The process of heterokaryosis, caused by merging of two hyphae belonging to different individuals, by a process called anastomosis , followed by a series of events resulting in genetically different cell nuclei in the mycelium . The merging of nuclei is not followed by meiotic events , such as gamete formation and results in an increased number of chromosomes per nuclei. Mitotic crossover may enable recombination , i.e., an exchange of genetic material between homologous chromosomes . The chromosome number may then be restored to its haploid state by nuclear division , with each daughter nuclei being genetically different from

12075-400: The proportions become approximately equal, and adults examined contained 27% diploid, 71% tetraploid and 2% octaploid nuclei. There is continued study and debate regarding the fitness advantages or disadvantages conferred by different ploidy levels. A study comparing the karyotypes of endangered or invasive plants with those of their relatives found that being polyploid as opposed to diploid

12190-684: The rest of the body being diploid (as in the mammalian liver ). For many organisms, especially plants and fungi, changes in ploidy level between generations are major drivers of speciation . In mammals and birds, ploidy changes are typically fatal. There is, however, evidence of polyploidy in organisms now considered to be diploid, suggesting that polyploidy has contributed to evolutionary diversification in plants and animals through successive rounds of polyploidization and rediploidization. Humans are diploid organisms, normally carrying two complete sets of chromosomes in their somatic cells: one copy of paternal and maternal chromosomes, respectively, in each of

12305-450: The same organism . 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. It is a major topic of cytology. Dihaploid and polyhaploid cells are formed by haploidisation of polyploids, i.e., by halving

12420-462: The same organism, and at different stages in an organism's life cycle. Half of all known plant genera contain polyploid species, and about two-thirds of all grasses are polyploid. Many animals are uniformly diploid, though polyploidy is common in invertebrates, reptiles, and amphibians. In some species, ploidy varies between individuals of the same species (as in the social insects ), and in others entire tissues and organ systems may be polyploid despite

12535-494: The same species or at different stages of the life cycle . In some insects it differs by caste . In humans, only the gametes are haploid, but in many of the social insects , including ants , bees , and termites , males develop from unfertilized eggs, making them haploid for their entire lives, even as adults. In the Australian bulldog ant, Myrmecia pilosula , a haplodiploid species, haploid individuals of this species have

12650-759: The same species. Species of the Deuteromycota were classified as Coelomycetes if they produced their conidia in minute flask- or saucer-shaped conidiomata, known technically as pycnidia and acervuli . The Hyphomycetes were those species where the conidiophores ( i.e. , the hyphal structures that carry conidia-forming cells at the end) are free or loosely organized. They are mostly isolated but sometimes also appear as bundles of cells aligned in parallel (described as synnematal ) or as cushion-shaped masses (described as sporodochial ). Most species grow as filamentous, microscopic structures called hyphae or as budding single cells (yeasts). Many interconnected hyphae form

12765-514: The spores reach a suitable substrate, they germinate, form new hyphae, which restarts the fungal life cycle. The form of the ascus is important for classification and is divided into four basic types: unitunicate-operculate, unitunicate-inoperculate, bitunicate, or prototunicate. See the article on asci for further details. The Ascomycota fulfil a central role in most land-based ecosystems . They are important decomposers , breaking down organic materials, such as dead leaves and animals, and helping

12880-547: The suffix -somy (rather than -ploidy , used for euploid karyotypes), such as trisomy and monosomy . Homoploid means "at the same ploidy level", i.e. having the same number of homologous chromosomes . For example, homoploid hybridization is hybridization where the offspring have the same ploidy level as the two parental species. This contrasts with a common situation in plants where chromosome doubling accompanies or occurs soon after hybridization. Similarly, homoploid speciation contrasts with polyploid speciation . Zygoidy

12995-486: The terms haploid and diploid in 1905. Some authors suggest that Strasburger based the terms on August Weismann 's conception of the id (or germ plasm ), hence haplo- id and diplo- id . The two terms were brought into the English language from German through William Henry Lang 's 1908 translation of a 1906 textbook by Strasburger and colleagues. The term haploid is used with two distinct but related definitions. In

13110-409: The thallus of the fungus defines the shape of the symbiotic colony. Some dimorphic species, such as Candida albicans , can switch between growth as single cells and as filamentous, multicellular hyphae. Other species are pleomorphic , exhibiting asexual (anamorphic) as well as a sexual (teleomorphic) growth forms. Except for lichens, the non-reproductive (vegetative) mycelium of most ascomycetes

13225-822: The yeasts and yeast-like fungi that have now been placed into the Saccharomycotina or Taphrinomycotina , while the Euascomycetes included the remaining species of the Ascomycota, which are now in the Pezizomycotina , and the Neolecta , which are in the Taphrinomycotina. Some ascomycetes do not reproduce sexually or are not known to produce asci and are therefore anamorphic species. Those anamorphs that produce conidia (mitospores) were previously described as mitosporic Ascomycota . Some taxonomists placed this group into

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