Sunday, February 05, 2006

Reproduction

The wide variety of fungi demonstrate many reproductive methods. In general, most fungi reproduce by making tiny spores. Fungi typically produce large numbers of spores. A giant puffball, for example, produces an estimated 7 trillion spores.

Fungi typically follow a reproductive cycle that involves the production of sexual spores. These spores contain one or more nuclei and are usually haploid—that is, their nuclei contain one set of chromosomes. When environmental conditions are favorable, the spores germinate and develop into a mycelium that produces fruiting bodies with enormous numbers of sexual spores, which repeat the reproductive cycle. Some fungi produce asexual spores directly from hyphae, which then germinate to produce additional mycelium. The mycelium spreads rapidly, aiding the fungus in dispersal and colonization.

In the reproductive cycle of mushrooms, the mycelium contain hyphae of two mating types, sometimes called plus and minus strains, with no obvious anatomical differences distinguishing them. If plus and minus strains of hyphae fuse, sexual reproduction begins. Initially the nuclei of the two hyphae remain separate, producing an intermediate stage called the dikaryon, meaning “two nuclei.” The dikaryon stage can last from weeks to years, depending upon the species. The two nuclei in the dikaryon eventually fuse to produce a diploid cell—that is, a cell that contains one nucleus with two sets of chromosomes. This cell immediately undergoes meiosis, a type of nuclear cell division that produces offspring with half the genetic material as the parents. Meiosis usually produces four genetically unique haploid spores and the reproductive cycle begins again. This population of genetically different spores has a better chance of surviving environmental changes, such as disease or temperature changes, that may wipe out an entire population of genetically identical spores.

Many fungi can reproduce by the fragmentation of their hyphae. Each fragment develops into a new individual. Yeast, a type of unicellular fungus, reproduce by budding, in which a bump forms on the yeast cell, eventually partitioning from the cell and growing into a new yeast cell.

more info at: oralthrushandcandidaalbicans.htm

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