大學(xué)生物專業(yè)英語lessonth-資料下載頁
2025-01-13 19:15本頁面
【正文】 ring anaphase I the two chromatids of each chromosome stay joined at the centromere and move together to one of the two poles of the cell. 但是 ， 與有絲分裂后期不同的是 ， 在后期 I， 每組染色體的兩個(gè)染色單體連接在著絲點(diǎn)上并一起移向細(xì)胞兩極的一極 。 It is this event that results in the halving of the chromosome number in the four daughter cells that result from meiosis. 由此而導(dǎo)致 4個(gè)子細(xì)胞中染色體數(shù)減半 。 College of Life Sciences Hubei Normal University 2022/2/10 41 During telophase I nuclear envelopes enclose the chromosomes in nuclei, and in most species cytokinesis (the first nuclear division) follows. 在末期 I， 核被膜圍繞著細(xì)胞核里的染色體 ， 在大多數(shù)物種里第一次 胞質(zhì)分裂緊隨其后 ． The second nuclear division begins with metaphase II, in which the chromosomes in each daughter cell again align on a metaphase plate． 第二次核分裂開始于分裂中期 II ， 子細(xì)胞中染色體再次重新排列在赤道板上 。 College of Life Sciences Hubei Normal University 2022/2/10 42 The centromeres finally divide, and each sister chromatid moves to one of the poles of the spindle. 著絲粒最終分離 ， 每個(gè)姊妹染色單體移向兩極 。 The next phase is telophase II, followed again by cytokinesis. 下一個(gè)時(shí)期是末期 II， 緊接著是第二次 胞質(zhì)分裂 。 The result of the entire process is four haploid cells in which parental chromosomes are randomly distributed. 整個(gè)減數(shù)分裂過程 ， 產(chǎn)生 4個(gè)親本染色體隨機(jī)分配的單倍體細(xì)胞 。 College of Life Sciences Hubei Normal University 2022/2/10 43 6. Asexual versus sexual reproduction 無性和有性生殖 College of Life Sciences Hubei Normal University 2022/2/10 44 Mitosis and meiosis, respectively, make simple cell division and sexual reproduction possible . 有絲分裂和減數(shù)分裂分別可以讓簡單的細(xì)胞分裂和有性生殖成為可能 。 Each means of passing on hereditary information has advantages. 每種傳遞遺傳信息的方式各有優(yōu)勢 。 College of Life Sciences Hubei Normal University 2022/2/10 45 In asexual reproduction the parent anism gives rise to offspring that are geic clones of the plement, requires little or no specialization of reproductive ans, and is more rapid than sexual reproduction. 在無性生殖中 ， 子 細(xì)胞就是親本的克隆 ， 保留了親本的遺傳信息 ， 親本不需要生殖器官的特化 ， 比有性生殖快的多 。 College of Life Sciences Hubei Normal University 2022/2/10 46 A major disadvantage of the asexual mode is that a single catastrophic event or disease may destroy an entire population of geically identical anisms. 無性生殖的一個(gè)主要的劣勢是 ， 一個(gè)簡單災(zāi)難性事件或疾病都可能摧毀遺傳上一致的整個(gè)種群 。 College of Life Sciences Hubei Normal University 2022/2/10 47 A prime benefit of sexual reproduction is that it provides geic variability and a ready mechanism for the elimination of deleterious mutations. 有性生殖的首要優(yōu)勢是它提供了遺傳變異和現(xiàn)存排除有害突變的機(jī)制 。 It also allows “new” gene forms to arise and spread through populations. 它也可以產(chǎn)生新的基因并在種群中傳遞 (蔓延 )。 College of Life Sciences Hubei Normal University 2022/2/10 48
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