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An ascus (from Ancient Greek ἀσκός (askós) 'skin bag, wineskin'; pl.: asci) [1] is the sexual spore-bearing cell produced in ascomycete fungi. Each ascus usually contains eight ascospores (or octad), produced by meiosis followed, in most species, by a mitotic cell division.
The ascus is a diagnostic morphological feature of the bryozoan suborder Ascophora (hence the name of the suborder). [1] It is a water-filled sac of frontal membrane opening (ascopore) at or near the zooid orifice.
Ascus (Ancient Greek: Ἄσκος) was a giant from ancient Greek mythology, who in conjunction with Lycurgus of Thrace chained the god Dionysus and threw him into a river. The god Hermes (or, according to other tellings, Zeus ) rescued Dionysus, conquered (ἐδαμασεν) the giant, flayed him, and made a bag (ἄσκος) of his skin.
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 is a tube-shaped vessel, a meiosporangium, which contains the sexual spores produced by meiosis and which are called ascospores.
The eight ascospores are produced inside an ascus. Sordaria squashes can give us information about crossing over during meiosis. If no crossing over occurs a 4:4 pattern is produced: four black spores, and four tan spores all lined up. If crossing over does occur there is a 2:2:2:2 pattern visible, or a 2:4:2 pattern.
Pezizomycotina is the largest subdivision of Ascomycota, containing the filamentous ascomycetes and most lichenized fungi. It is more or less synonymous with the older taxon Euascomycota. [2]
The ascus itself forms as a radiating spur branch at the top of the hook. Each nucleus divides, resulting in the formation of a pair of compatible nuclei, i.e. a dikaryon, in the ascus, which is now the penultimate space. Two sister nuclei remain, one in the basal cell and the other in the crozier tip.
Ascophora is an infraorder under order Cheilostomatida of the Bryozoa.. They are now considered a synonym of Flustrina. [1]Ascophorans are distinguished from other cheilostomes in having a completely calcified wall covering their frontal surface apart from the orifice, and possessing an ascus (hence the name of the suborder).