1、Chapter 2Mitosis and Meiosis,Maintenance of Genetic Continuity Between Cells and Organisms,Mitosis(有絲分裂) Two genetically identical, generally diploid(二倍體) cells (same as parent cell) Meiosis(減數(shù)分裂) Reduction division produces progeny(后代) cells with one-half the genetic content and number of chromosom

2、es as parent cell Produces gametes配子 /spores孢子 for sexual reproduction,2.1 Cell structure,線粒體,細(xì)胞質(zhì),溶酶體,滑面內(nèi)質(zhì)網(wǎng),游離核糖體,中心體,核糖體,粗面型內(nèi)質(zhì)網(wǎng),質(zhì)膜,細(xì)胞外被,細(xì)胞核,核仁,染色質(zhì),核膜孔,核膜,高爾基體,Glycocalyx ,laikukeiliks (細(xì)胞外被的)多糖蛋白質(zhì)復(fù)合物,Heterochromatin(異染色質(zhì)): The heavily staining, late replicating regions of chromosomes that are conde

3、nsed during the interphase of cell cycle.,Euchromatin(常染色質(zhì)): Chromatin or chromosomal regions that are lightly staining and are relatively uncoiled during the interphase of cell cycle.,Nucleus,兩種染色質(zhì)的區(qū)別,端粒,異染色質(zhì),著絲粒,常染色質(zhì),姐妹染色單體,短臂,長(zhǎng)臂,2.2 Chromosomes exist in Homologous Pairs in Diploid Organisms,Chrom

4、osome in eukaryotes,petit,Chromosomes differ in size and morphology(形態(tài)) . Each has a constriction called a centromere(著絲粒) that is used in segregation during mitosis and meiosis.,中著絲粒染色體,近中著絲粒染色體,近端著絲粒染色體,端著絲粒染色體,Specialized Chromosomes Polytene Chromosomes(多線染色體),Polytene chromosomes are giant chro

5、mosomes consisting of many identical strands, The bands of polytene chromosomes were usually concerned as the visible manifestation of genes. 中文定義：雙翅目昆蟲的幼蟲唾腺細(xì)胞，多條染色質(zhì)（5001000條染色線）重疊成類似染色體狀結(jié)構(gòu)。,Specialized Chromosomes Lampbrush Chromosomes(燈刷染色體),Lampbrush chromosomes are meiotic chromosomes characteri

6、zed by extended lateral loops, which reach maximum extension during diplotene（雙線期) . 中文定義：兩棲類未成熟的卵母細(xì)胞第一次減數(shù)分裂停留在雙線期的染色體。是RNA合成的活躍場(chǎng)所。一個(gè)側(cè)環(huán)是一個(gè)轉(zhuǎn)錄單位。,Bacterial Chromosome 細(xì)菌染色體,The chromosomes of bacteria are much less complicated than eukaryotes真核生物 do. They usually consist of a double stranded nucleic a

7、cid molecular, exist as circular form, and are compacted into a structure sometimes referred to as the nucleoid(類核) .,Viral（病毒的） Chromosome,Viral chromosomes chemically may contain either DNA or RNA. The DNA containing viral chromosomes may be either of linear shape or circular shape. The RNA contai

8、ning viral chromosomes are composed of a linear, single-stranded RNA molecule and occur in some animal viruses, most plant viruses and some bacteriophages.,一些生物的染色體數(shù)目,Homologous chromosomes, haploidy, and diploidy,Homologous chromosomes(同源染色體): Chromosomes that pair(synapse聯(lián)會(huì)) in meiosis and have th

9、e same genetic loci and structure. One member of each pair is derived from the materal parent and the other is derived from the pateral parent. Sex-determining chromosomes are important exception to the concept of homologous pairs of chromosomes.,Haploid(單倍體): a cell or organism(生物體) containing the

10、set of chromosomes normally found in gametes. The total set of genes contained in a haploid set of chromosomes constitutes the genome of the species. Diploid(二倍體): a cell or organism with two complete sets of homologous chromosomes. Diploid cells are produced by haploid (N) gametes that fuse to form

11、 a zygote(受精卵) . The zygote then undergoes development, forming a new individual.,Genome (基因組)(P21):the total collection of genes/genetic material of an organism (haploid set. Locus/loci(基因座) (P21): the site or place on a chromosome where a particular gene is located. allele (等位基因) (P21): one of the

12、 possible states of a gene. karyotype(核型) (P21): the chromosome complement of a cell or an individual.,染色體的核型(karyotype) 一個(gè)物種的一組染色體所具有的特定的染色體的大小，形態(tài)和數(shù)目。 核型分析：根據(jù)染色體數(shù)目、大小和著絲粒位置、臂比、次縊痕、隨體等形態(tài)特征，對(duì)生物核內(nèi)染色體進(jìn)行配對(duì)、分組、歸類、編號(hào)、進(jìn)行分析的過程。,Eg 蠶豆的核型分析,2n=12， 染色體長(zhǎng)度：大小 臂比：大小 帶型：同源編號(hào),2.3 Mitosis Partitions Chromosomes into

13、 Dividing Cells,Mitosis is critical to all eukaryotes(真核生物) as a mechanism to produce new cells Allows for asexual(無(wú)性生殖) reproduction Protozoans(原生動(dòng)物) , fungi(菌類) , algae(藻類) Partitions chromosomes equally into “daughter” cells Multicellular eukaryotes begin life as a zygote (受精卵) Mitosis produces a

14、ll of the cells required for the adult form,cytokinesis,Cell growth,DNA replication: Chromosomes duplicate,Cell prepares to divide,chromosome copies separate,Cytoplasm divides,Cell division composed of: 1、Karyokinesis(核分裂 )(P22): process of nuclear division (division of genetic material).2、Cytokines

15、is(胞質(zhì)分裂)(P22) : process of dividing cytoplasm/cell.,Interphase（間期） Composed of: (1) Gap 1 (G1) when the cell prepares for chromosome replication. (2) Synthesis (S) when DNA replicates and new chromosomes are formed. (3) Gap 2 (G2) when the cell prepares for mitosis and cell division.,Relative time i

16、n each phase varies among cell types, with duration of G1 generally the deciding factor. Some cells exit G1 and enter a nondividing state called G0. Interphase chromosomes are elongated and hard to see with light microscopy. Sister chromatids are held together by replicated but unseparated centromer

17、es.,Mitosis stages Mitosis is a continuous process, but geneticists divide it into four distinguishable stages: Prophase (前期) Metaphase (中期) Anaphase (后期) Telophase (末期),動(dòng)粒,前中期,i. The mitotic spindle（紡錘 體）, composed of microtubules（微管 ） made of tubulins（微管蛋白 ）, begins to form. ii. The nucleoli（核仁，nu

18、cleolus的復(fù)數(shù)） in the nucleus cease to be discrete areas. iii. The nuclear envelope breaks down. iv. Kinetochores（動(dòng)粒） form on the centromeres (著絲粒) and become attached to kinetochore microtubules（動(dòng)粒微管）.,Prophase(前期)is characterized by chromosomes condensing to a form visible by light microscopy,Metapha

19、se(中期)begins when the nuclear envelope has completely disappeared.,i. The kinetochore（動(dòng)粒） microtubules orient the chromosomes with their centromeres in a plane between the spindle poles, the metaphase plate. ii. The chromosomes reach a highly condensed state.,Anaphase(后期)begins when the centromeres

20、of the sister chromatids separate.,i. The chromatids separate (disjunction) and daughter chromosomes move toward opposite poles by kinetochore microtubules. ii. Shape of the chromosomes moving toward the poles is defined by their centromere locations. iii. Cytokinesis (胞質(zhì)分裂) usually begins near the

21、end of anaphase.,Telophase (末期) is when migration of daughter chromosomes is completed.,i. Chromosomes begin to uncoil and form interphase chromosomes. ii. Nuclear envelope forms around each chromosome group. iii. Spindle microtubules disappear. iv. Nucleoli reform. v. Nuclear division is complete.,

22、Cytokinesis (胞質(zhì)分裂) （P25),Cytokinesis is division of the cytoplasm, compartmentalizing（劃分 ） the new nuclei into separate daughter cells. In animal cells, cytokinesis begins with a constriction in the center of the cell, which develops until two new cells are produced. Most plant cells form a cell pla

23、te (membrane and wall) between the two nuclei, resulting in two progeny cells,Animal Cell Cytokinesis,Microfilaments contract,Cleavage furrow,微絲,卵裂溝,cell wall,former spindle equator,cell plate,Plant Cell Cytokinesis,細(xì)胞板,有絲分裂的特點(diǎn)：染色體復(fù)制1次，細(xì)胞分裂1次，子細(xì)胞與母細(xì)胞一樣。 有絲分裂的意義： 1.保證了細(xì)胞上下代之間遺傳物質(zhì)的穩(wěn)定性和連續(xù)性。 2.維持個(gè)體的正常生長(zhǎng)

24、和發(fā)育 分裂 數(shù)量 個(gè)體發(fā)育 細(xì)胞 分化 種類,前期： 染色質(zhì)細(xì)長(zhǎng)如絲、開始濃縮，核膜、核仁變淡。 中期： 染色體，著絲粒排列，紡錘體形成，觀察最佳。 后期： 著絲粒一分為二。 末期： 核仁出現(xiàn) 赤道面細(xì)胞板 兩極分離子細(xì)胞形成。 染色體數(shù)目未變,小結(jié)：有絲分裂過程,2.4 Meiosis 染色質(zhì)細(xì)長(zhǎng)如絲,In zygonema(偶線期), the synaptonemal complex（聯(lián)會(huì)復(fù)合體） begins to form and synapsis occurs. Synapsis is referred to a tight association between homologo

25、us chromosomes. 偶線期：同源染色體配對(duì)（聯(lián)會(huì)）；聯(lián)會(huì)復(fù)合體；二價(jià)體-四條單體,In pachynema (粗線期), crossing-over(交換), which can result in genetic exchange between members of each homolog(nonsister chromatids非姐妹染色單體), occurs. 粗線期：非姊妹染色單體間交換重組,Diplonema (雙線期) is when chromosomes begin to move apart, and chiasmata (交叉) (singular is c

26、hiasma) formed by crossing-over become visible. 雙線期：聯(lián)會(huì)的同源染色體相互排斥、開始分離，但在交叉點(diǎn)(chiasma)上還保持著聯(lián)系。交叉結(jié)向末端移動(dòng)并逐漸減少，稱為交叉端化。,Diakinesis (終變期) involves breakdown of the nucleoli（核仁 ） and nuclear envelope, and assembly of the spindle. In addition, the chromosomes pull farther apart and a process called terminali

27、zation（末端化 ） is completed during this stage. 終變期：交叉完全端化,1,2,3,4,交換,Metaphase I (中期I),The nuclear envelope completely broken down. Chromosomes maximally thickened Nonsister chromatids associated at terminal chiasma (交叉) Only bivalents (pairs of homologs) aligned at the equatorial plane（赤道板） The spind

28、le completely formed, and microtubules attached to kinetochores（動(dòng)粒 ） 中期I的主要特點(diǎn)是染色體排列在赤道面上。,Anaphase I (后期I ),Anaphase I is when bivalents separate, with chromosomes of each homologous pair disjoining. Resulting dyads (二分體 ) migrate toward opposite poles, where new nuclei will form. This migration ass

29、umes that: i. Centromeres(著絲粒 ) derived from each parent will migrate randomly toward each pole. ii. Each pole will receive a haploid complement of replicated centromeres with associated chromosomes. iii. Sister chromatids (姊妹染色單體) will remain attached to each other (the major difference from mitosi

30、s). 后期I：同源染色體彼此分離，分別向兩極移動(dòng)。染色體數(shù)目減半。 同源染色體隨機(jī)分向兩極，使母本和父本染色體重所組合，產(chǎn)生基因組的變異。,Telophase I (末期I ),Telophase I has dyads completing migration to the poles, and usually formation of a nuclear envelope around each haploid grouping. Cytokinesis(胞質(zhì)分裂 ) follows in most species, forming two haploid cells. But cell

31、s may either go directly to meiosis II or have short interphase (but no further DNA replication) 末期I：染色體到達(dá)兩極后，解旋為細(xì)絲狀、核膜重建、核仁形成，同時(shí)進(jìn)行胞質(zhì)分裂。,Meiosis II,Prophase II involves chromosome condensation. 每條染色體含2條姊妹染色單體,染色體數(shù)是n 。 Metaphase II includes spindle formation, with centromeres lining up on the equator

32、. 染色體著絲粒排列在赤道板上。 Anaphase II involves splitting of the centromeres, with chromosomes pulled to opposite poles. 著絲粒縱裂,姊妹染色單體向兩極移動(dòng)。 Telophase II takes place as a nuclear envelope forms around each set of chromosomes. 核膜重新形成。 Cytokinesis usually takes place, and chromosomes become elongated and invisible with light microscopy.,減數(shù)分裂的特點(diǎn)： 染色體復(fù)制1次，細(xì)胞連續(xù)分裂2次， 1次分裂1個(gè)細(xì)胞形成4個(gè)細(xì)胞，子細(xì)胞染色體是母細(xì)胞一半。,減數(shù)分裂的意義,1.遺傳：保證了物種的相對(duì)穩(wěn)定性：,2.變異:為子代的變異提供了物質(zhì)基礎(chǔ)，有利于進(jìn)化： 后期I同源染色體的成員移向兩極是隨