第五章 Chromosomes: Where are the Genes Found? 前言.

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1 第五章 Chromosomes: Where are the Genes Found? 前言

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3 chromosome (unduplicated) in a cell at interphase
same chromosome (duplicated) in interphase prior to mitosis mitosis, cytoplasmic division Fig. 8.6, p. 131 chromosome (unduplicated) in a daughter cell at interphase chromosome (unduplicated) in a daughter cell at interphase

4 分裂的細胞: 世代間的橋樑 分裂機制的概觀 有關染色體的要點 有絲分裂與染色體的數目

5 細胞的分裂 有絲分裂 (Mitosis) vs. 減數分裂 (Meiosis) 體細胞 (Somatic cell) vs. 生殖細胞 (Germ cell)

6 Prokaryotic organisms
Division Mechanisms Eukaryotic organisms Mitosis Meiosis Prokaryotic organisms Prokaryotic fission

7 Roles of Mitosis Multicelled organisms
Growth Cell replacement Some protistans, fungi, plants, animals Asexual reproduction

8 細看染色體 姊妹染色分體 著絲粒

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10 Organization of Chromosomes
DNA one nucleosome DNA and proteins arranged as cylindrical fiber histone

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14 One nucleosome DNA core of histone Fig. 8.3, p. 129

15 單套 (Haploid) vs. 雙套 (Diploid)
有絲分裂與染色體的數目 單套 (Haploid) vs. 雙套 (Diploid) Sum total of chromosomes in a cell Somatic cells Chromosome number is diploid (2n) Two of each type of chromosome Gametes Chromosome number is haploid (n) One of each chromosome type

16 Human Chromosome Number
Diploid chromosome number (n) = 46 Two sets of 23 chromosomes each One set from father One set from mother Mitosis produces cells with 46 chromosomes--two of each type

17 Lots of DNA Stretched out, the DNA from one human somatic cell would be more than two meters long A single line of DNA from a salamander cell would extend for ten meters

18 細胞週期 (Cell Cycle)

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21 Spindle Apparatus one spindle pole one of the condensed chromosomes
spindle equator microtubules organized as a spindle apparatus one spindle pole

22 Interphase Usually longest part of the cycle Cell increases in mass
Number of cytoplasmic components doubles DNA is duplicated

23 Stages of Interphase G1 S G2 Interval or gap after cell division
Time of DNA synthesis (replication) G2 Interval or gap after DNA replication

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25 Control of the Cycle Once S begins, the cycle automatically runs through G2 and mitosis The cycle has a built-in molecular brake in G1 Cancer involves a loss of control over the cycle, malfunction of the “brakes”

26 Stopping the Cycle Some cells normally stop in interphase
Neurons in human brain Arrested cells do not divide Adverse conditions can stop cycle Nutrient-deprived amoebas get stuck in interphase

27 有絲分裂之階段 前期 (Prophase) 中期 (Metaphase) 後期 (Anaphase) 末期 (Telophase)

28 前期:有絲分裂之開始

29 過度到中期 後期到末期

30 胞質分裂 (Cytokinesis; Cytoplasmic division) 植物有細胞板的形成 動物細胞的胞質分裂

31 植物: 細胞板 (Cell plate) 的形成

32 動物細胞的胞質分裂 分割溝 (Cleavage furrow)

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34 Culturing Cells Growing cells in culture allows researchers to investigate processes and test treatments without danger to patients Most cells cannot be grown in culture

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36 減數分裂 前言: 托鞋笠貝(Slipper limpet)的故事 芽蟲 (Aphids)的故事

37 托鞋笠貝 (Slipper limpet) 芽蟲 (Aphids)

38 Sexual Reproduction 有性生殖與無性生殖的比較
Chromosomes are duplicated in germ cells Germ cells undergo meiosis and cytoplasmic division Cellular descendents of germ cells become gametes Gametes meet at fertilization

39 Asexual Reproduction 有性生殖與無性生殖的比較 Single parent produces offspring
All offspring are genetically identical to one another and to parent

40 Sexual Reproduction Involves
Meiosis Gamete production Fertilization Produces genetic variation among offspring

41 Homologous Chromosomes Carry Different Alleles
Cell has two of each chromosome One chromosome in each pair from mother, other from father Paternal and maternal chromosomes carry different alleles

42 Sexual Reproduction Shuffles Alleles
Through sexual reproduction, offspring inherit new combinations of alleles, which leads to variations in traits This variation in traits is the basis for evolutionary change

43 Gamete Formation Gametes are sex cells (sperm, eggs)
Arise from germ cells

44 Chromosome Number 減數分裂(Meiosis)使染色體數目 (Chromosome number)減半
Sum total of chromosomes in a cell Germ cells are diploid (2n) Gametes are haploid (n) Meiosis halves chromosome number

45 物種 雙套染色體數 果蠅 8 豌豆 14 玉米 20 青蛙 26 蚯蚓 36 人類 46 猩猩 48 阿米巴變形蟲 50 木賊 216

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48 減數分裂是兩次分裂,不是一次 Two consecutive nuclear divisions
Meiosis I Meiosis II DNA is NOT duplicated between divisions Four haploid nuclei are formed

49 Meiosis I Each homologue in the cell pairs with its partner,
then the partners separate

50 Meiosis II The two sister chromatids of each duplicated chromosome are separated from each other two chromosomes (unduplicated) one chromosome (duplicated)

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52 減數分裂各時期

53 減數分裂各時期

54 減數分裂的重要事件 前期 中期 (排列)

55 前期

56 中期 (排列)

57 從配子到子代 植物的配子形成 動物的配子形成

58 植物的配子形成

59 動物的配子形成: 精子形成(Spermatogenesis)與卵子形成(Oogenesis)

60 精子形成(Spermatogenesis)

61 卵子形成(Oogenesis)

62 減數分裂與有絲分裂之比較

63 減數分裂與有絲分裂之比較

64 減數分裂與有絲分裂之比較

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66 授精作用(Fertilization) 恢復染色體數目 有更多的遺傳特性之交換

67 Crossing Over Each chromosome becomes zippered to its homologue
All four chromatids are closely aligned Non-sister chromosomes exchange segments

68 Effect of Crossing Over
After crossing over, each chromosome contains both maternal and parental segments Creates new allele combinations in offspring

69 Random Alignment During transition between prophase I and metaphase I, microtubules from spindle poles attach to kinetochores of chromosomes Initial contacts between microtubules and chromosomes are random Either the maternal or paternal member of a homologous pair can end up at either pole The chromosomes in a gamete are a mix of chromosomes from the two parents

70 Possible Chromosome Combinations
As a result of random alignment, the number of possible combinations of chromosomes in a gamete is: 2n (n is number of chromosome types)

71 Possible Chromosome Combinations
1 2 3 Possible Chromosome Combinations or or or