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As a result, the ascus will contain four pairs of spores. Then the ascospores are released from the ascus. In many cases the asci are formed in a regular layer, the hymenium, in a fruiting body which is visible to the naked eye, here called an ascocarp or ascoma. In other cases, such as single-celled yeasts, no such structures are found.
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.
Here the fertile layer is free, so that many spores can be dispersed simultaneously. The morel, Morchella, an edible ascocarp, not a mushroom, favored by gourmets, is a mass of apothecia fused together in a single large structure or cap. The genera Helvella and Gyromitra are similar.
There are 2000 identified genera and 30,000 species of Ascomycota. The unifying characteristic among these diverse groups is the presence of a reproductive structure known as the ascus, though in some cases it has a reduced role in the life cycle. Many ascomycetes are of commercial importance.
Their perithecia are superficial to completely immersed in the substrate, and oriented at right angles to the surface of the stroma. The asci are cylindrical with a thickened ascus tip. Ascospores are usually cylindrical, contain multiple septa, and disarticulate into part-spores or remain intact at maturity. [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.
The generic name polyascus (poly "many" + ascus "bag") refers to the typical presence of multiple external sac-like female bodies, known as externae. In Polyascus species, these originate from asexual reproduction. [1]
The perithecia have short pseudoparaphyses; [39] these vertical, filament-like support structures are similar to paraphyses but grow downwards in the perithecial cavity before ascus formation. [40] In two genera, Endocarpon and Staurothele , algal cells occur in the hamathecium. [ 39 ]