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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Parasexual cycle ： ウィキペディア英語版 Parasexual cycle The parasexual cycle, a process peculiar to fungi and single-celled organisms, is a nonsexual mechanism of parasexuality for transferring genetic material without meiosis or the development of sexual structures.〔Alexopolous (1996), ''et al''., pp. 196–97.〕 It was first described by Italian geneticist Guido Pontecorvo in 1956 during studies on ''Aspergillus nidulans'' (also called ''Emericella nidulans'' when referring to its sexual form, or teleomorph). A parasexual cycle is initiated by the fusion of hyphae (anastomosis) during which nuclei and other cytoplasmic components occupy the same cell (heterokaryosis and plasmogamy). Fusion of the unlike nuclei in the cell of the heterokaryon results in formation of a diploid nucleus (karyogamy), which is believed to be unstable and can produce segregants by recombination involving mitotic crossing-over and haploidization. Mitotic crossing-over can lead to the exchange of genes on chromosomes; while haploidization probably involves mitotic nondisjunctions which randomly reassort the chromosomes and result in the production of aneuploid and haploid cells. Like a sexual cycle, parasexuality gives the species the opportunity to recombine the genome and produce new genotypes in their offspring. Unlike a sexual cycle, the process lacks coordination and is exclusively mitotic. The parasexual cycle resembles sexual reproduction. In both cases, unlike hyphae (or modifications thereof) may fuse (plasmogamy) and their nuclei will occupy the same cell. The unlike nuclei fuse (karyogamy) to form a diploid (zygote) nucleus. In contrast to the sexual cycle, in the parasexual cycle recombination takes place during mitosis followed by haploidization (but without meiosis). The recombined haploid nuclei appear among vegetative cells, which differ genetically from those of the parent mycelium. Both heterokaryosis and the parasexual cycle are very important for those fungi that have no sexual reproduction. Those cycles provide for somatic variation in the vegetative phase of their life cycles. This is also true for fungi where the sexual phase is present, although in this case, additional and significant variation is incorporated through the sexual reproduction. ==Stages== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Parasexual cycle」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.