【正文】 ivision of the cell cytoplasm at the end of mitosis is called cytokinesis. 在有絲分裂結束時 ， 細胞質(zhì)的分裂稱為胞質(zhì)分裂 。 In animal cells it takes place as a ring of actin filaments contracts around the cell equator, pinching the cell in two. 在動物細胞中 ， 環(huán)形的肌動蛋白 纖維圍繞赤道板收縮 ，將細胞一分為二 。 College of Life Sciences Hubei Normal University 2022/2/10 31 In plant cells, which are bounded by a cell wall, cytokinesis involves the building of a new cell plate across the dividing cell at its equator. 在植物細胞中 ， 被細胞壁包圍 ， 胞質(zhì)分裂涉及到 在 正在分裂的細胞的赤道板上 新的細胞板的形成 。 (在植物細胞中 ， 在赤道板形成新的細胞板 。 ) Cell wall material is then deposited in the region of the cell plate. 然后 ， 細胞壁材料在細胞板區(qū)域沉積 ． College of Life Sciences Hubei Normal University 2022/2/10 32 Actin and Myosin and Cytokinesis Operation of the Contractile Ring during Cytokinesis College of Life Sciences Hubei Normal University 2022/2/10 33 5. Meiosis: the basis of sexual reproduction 減數(shù)分裂：有性生殖的基礎 College of Life Sciences Hubei Normal University 2022/2/10 34 Meiosis is a special form of cell division that takes place in the reproductive ans that produce sex cells. 減數(shù)分裂是發(fā)生在產(chǎn)生性細胞的生殖器官中的一種特殊的分裂形式 。 (減數(shù)分裂是性細胞分裂的特殊形式 。 ) Like mitosis, it takes place after DNA replication has occurred and involves two sequential nuclear divisions (meiosis I and meiosis II). 如有絲分裂 ， 它也是發(fā)生在 DNA復制后 ， 并有兩個連續(xù)的核分裂 。 College of Life Sciences Hubei Normal University 2022/2/10 35 These division results in four daughter cells, each with half the number of chromosomes of the parent cell. 減數(shù)分裂產(chǎn)生 4個子細胞 ， 分別含有親本一半的染色體數(shù) 。 The phenomenon of crossing over during meiosis results in exchange of geic information between chromosomes. 在減數(shù)分裂中的交換現(xiàn)象導致染色體之間的遺傳信息交換 。 College of Life Sciences Hubei Normal University 2022/2/10 36 Hence, the homologous chromosome distributed to different progeny cells are not identical. 因此，分配到不同子細胞中的同源染色體是不相同的。 College of Life Sciences Hubei Normal University 2022/2/10 37 College of Life Sciences Hubei Normal University 2022/2/10 38 As in mitosis two chromatids exist for each chromosome at the beginning of prophase I. 正如在有絲分裂中一樣 ， 在前期 I開始的時候每個染色體是以兩個染色單體形式存在 ． College of Life Sciences Hubei Normal University 2022/2/10 39 During this phase the homologous chromosomes undergo synapsis, or pairing, which is brought about by a bridging structure of proteins and RNA called the synaptinemal plex. 在這個時期 ， 同源染色體通過蛋白質(zhì)和 RNA組成的聯(lián)會復合體進行聯(lián)會或配對 。 The homologous pairs stay together when they align on the metaphase plate. 同源染色體對一起成線形排列在中期赤道板上 。 College of Life Sciences Hubei Normal University 2022/2/10 40 Unlike the anaphase of mitosis, however, du