Editing Ascomycota (section)

==== Formation of sexual spores ====
The sexual part of the life cycle commences when two hyphal structures [[Mating|mate]]. In the case of ''[[homothallic]]'' species, mating is enabled between hyphae of the same fungal [[cloning|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 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 [[Allorecognition#Allorecognition phenomena|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 [[:wikt:trichogyne|trichogyne]] emerges from one gametangium, 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 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 [[genetic recombination|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 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.<ref name="Carlile">{{cite journal |last1=Carlile |first1=Michael J. |title=Two influential mycologists: Helen Gwynne-Vaughan (1879–1967) and Lilian Hawker (1908–1991) |journal=Mycologist |date=August 2005 |volume=19 |issue=3 |pages=129–131 |doi=10.1017/S0269-915X(05)00305-8 }}</ref>

[[File:Hypomyces chrysospermus.jpg|thumb|left|150px|Unitunicate-inoperculate Asci of ''Hypomyces chrysospermus'']]
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, 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:

* Naked asci: these occur in simple ascomycetes; asci are produced on the organism's surface.
* [[Ascocarp#Perithecium|Perithecia]]: Asci are in flask-shaped ascoma (perithecium) with a pore (ostiole) at the top.
* [[Ascocarp#Cleistothecium|Cleistothecia]]: The ascocarp (a cleistothecium) is spherical and closed.
* [[Ascocarp#Apothecium|Apothecia]]: The asci are in a bowl shaped ascoma (apothecium). These are sometimes called the "cup fungi". 
* [[Ascocarp#Pseudothecium|Pseudothecia]]: Asci with two layers, produced in pseudothecia that look like perithecia. The ascospores are arranged irregularly.<ref>{{Cite web|url=https://www.microscopemaster.com/ascomycota.html|title=Ascomycota – Characteristics, Nutrition and Significance|website=MicroscopeMaster|language=en|access-date=4 March 2019}}</ref>

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 the hyphae. The two nuclei contained in the apical part of each hypha divide in such a way that the threads of their [[mitotic spindle]]s 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 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.
[[File:Ascocarp2.png|thumb|right|alt=Cross-section of a cup-shaped structure showing locations of developing meiotic asci (upper edge of cup, left side, arrows pointing to two gray-colored cells containing four and two small circles), sterile hyphae (upper edge of cup, right side, arrows pointing to white-colored cells with a single small circle in them), and mature asci (upper edge of cup, pointing to two gray-colored cells with eight small circles in them)|Diagram of an [[apothecium]] (the typical cup-like reproductive structure of ascomycetes) showing sterile tissues as well as developing and mature asci.]]

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 [[ploidy#Haploid and monoploid|haploid]] nuclei, usually followed by 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&nbsp;cm. away. When 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 [[Ascus|asci]] for further details.