Brachymeiosis was a hypothesized irregularity in the sexual reproduction of ascomycete fungi, a variant of meiosis following an "extra" karyogamy (nuclear fusion) step. The hypothesized process would have transformed four diploid nuclei into eight haploid ones. The current scientific consensus is that brachymeiosis does not occur in any fungi.
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| - Brachymeiosis (en)
- 簡略減數分裂 (zh)
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| - 簡略減數分裂（Brachymeiosis）是子囊菌門真菌有性生殖中的一個假說，描述子囊菌在產生子囊時，比正常減數分裂多經過一次的過程。在此假說的描述中，子囊在產生子囊孢子時，當中的四個二倍體核會分裂成八個單倍體核。以目前的科學共識而言，簡略減數分裂並不存在於任何真菌中。 子囊菌會藉由形成雄配子囊及雌配子囊（即藏精器及藏卵器）來進行有性繁殖。藏精器會將單套的核傳給藏卵器，使藏卵器便成為具有兩個核的雙核子囊，接著子囊內會發生核融合並形成二倍體核，並經過一次減數分裂及一次有絲分裂後生成八個單倍體核的子囊孢子。1895年，在植物學家的報告中，觀察到子囊生成（ascogeny）之前藏卵器發生了第二次核融合。這意味著在子囊中會產生四倍體核，而非二倍體核；正常有絲分裂不會改變染色體的倍性，但為了產出單倍體核，子囊需要進行第二次的分裂以降低其倍性，這種分裂在西元1908年被H. C. I. Fraser稱為「簡略減數分裂」。 隨著許多與此假說矛盾的研究結果被發表，簡略減數分裂的存在於20世紀的上半世紀一直備受爭議。當更加進步的染色技術問世，研究人員們發現子囊中只發生一次減數分裂，且對於所有實驗物種，包含先前就已經被認為會進行簡略減數分裂的物種而言，都是如此。因此，這些描述雙重核融合的相關理論及簡略減數分裂假說便在西元1950年左右被捨棄。 (zh)
- Brachymeiosis was a hypothesized irregularity in the sexual reproduction of ascomycete fungi, a variant of meiosis following an "extra" karyogamy (nuclear fusion) step. The hypothesized process would have transformed four diploid nuclei into eight haploid ones. The current scientific consensus is that brachymeiosis does not occur in any fungi. (en)
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| - Brachymeiosis was a hypothesized irregularity in the sexual reproduction of ascomycete fungi, a variant of meiosis following an "extra" karyogamy (nuclear fusion) step. The hypothesized process would have transformed four diploid nuclei into eight haploid ones. The current scientific consensus is that brachymeiosis does not occur in any fungi. According to the current understanding, ascomycetes reproduce by forming male and female organs (antheridia/spermatia and ), transferring haploid nuclei from the antheridium to the ascogonium, and growing a dikaryotic ascus containing both nuclei. Karyogamy then occurs in the ascus to form a diploid nucleus, followed by meiosis and mitosis to form eight haploid nuclei in the ascospores. In 1895, the botanist R.A. Harper reported the observation of a second karyogamy event in the ascogonium prior to ascogeny. This would imply the creation of a tetraploid nucleus in the ascus, rather than a diploid one; in order to produce the observed haploid ascospores, a second meiotic reduction in chromosome count would then be necessary. The second reduction was hypothesized to occur during the second or third mitotic division in the ascus, even though chromosome reduction does not typically occur during mitosis. This supposed form of meiosis was termed “brachymeiosis” in 1908 by H. C. I. Fraser. The existence of brachymeiosis was controversial throughout the first half of the twentieth century, with many conflicting results published. Then, research with improved staining techniques established clearly that only one reductive division occurs in the asci of all examined species, including some which had been believed to undergo brachymeiosis. As a result of these studies, the theories of double fusion and subsequent brachymeiosis were discarded around 1950. (en)
- 簡略減數分裂（Brachymeiosis）是子囊菌門真菌有性生殖中的一個假說，描述子囊菌在產生子囊時，比正常減數分裂多經過一次的過程。在此假說的描述中，子囊在產生子囊孢子時，當中的四個二倍體核會分裂成八個單倍體核。以目前的科學共識而言，簡略減數分裂並不存在於任何真菌中。 子囊菌會藉由形成雄配子囊及雌配子囊（即藏精器及藏卵器）來進行有性繁殖。藏精器會將單套的核傳給藏卵器，使藏卵器便成為具有兩個核的雙核子囊，接著子囊內會發生核融合並形成二倍體核，並經過一次減數分裂及一次有絲分裂後生成八個單倍體核的子囊孢子。1895年，在植物學家的報告中，觀察到子囊生成（ascogeny）之前藏卵器發生了第二次核融合。這意味著在子囊中會產生四倍體核，而非二倍體核；正常有絲分裂不會改變染色體的倍性，但為了產出單倍體核，子囊需要進行第二次的分裂以降低其倍性，這種分裂在西元1908年被H. C. I. Fraser稱為「簡略減數分裂」。 隨著許多與此假說矛盾的研究結果被發表，簡略減數分裂的存在於20世紀的上半世紀一直備受爭議。當更加進步的染色技術問世，研究人員們發現子囊中只發生一次減數分裂，且對於所有實驗物種，包含先前就已經被認為會進行簡略減數分裂的物種而言，都是如此。因此，這些描述雙重核融合的相關理論及簡略減數分裂假說便在西元1950年左右被捨棄。 (zh)
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