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Chapter 5 cell division SPM Biology Form 4

Mitosis and meiosis

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Chapter 5 cell division SPM Biology Form 4

  1. 1. Chapter 5 Cell Division Ong Yee Sing 14/06/2017
  2. 2. Objectives • Identify the phases in a cell cycle • Understanding the processes of mitosis and meiosis • State the importance of mitosis and meiosis • Explain the importance of controlled mitosis • Understanding the process of cloning and its characteristics
  3. 3. Chromosomes • DNA are stored as chromosomes in the nucleus. • Chromosomal number is the characteristics number of chromosomes of a species. • In some cases, chromosomes can be found in pair, which share the same structure, referred as homologous chromosomes. • Somatic cells of a diploid organisms contain two pair of chromosome (2n). • Gametes or haploid organisms contain only one set of chromosome (n). 染色体 染色体数 同源染色体 二倍体体细胞 配子 单倍体
  4. 4. Karyotype • A karyotype is the number and appearance of chromosomes in the nucleus of a eukaryotic cell. A female genome visualized with fluorescent in situ hybridization (FISH). Karyotype variability in different cultivars of maize demonstrated using FISH. 核型
  5. 5. The cell cycle • The cell cycle is a cyclic sequences of events that a cell undergoes, from the time it is formed until it divides completely into two. • Two main phrases in the cell cycle is: • Interphase 间期 – cell grows and prepares for cell division • Cell division (M phase) – cell divides its nucleus and cytoplasm 细胞周期 循环
  6. 6. Interphase • Interphase can be divides into G1, S and G2 phases. 间期
  7. 7. G1 phase • The first gap phase where the chromosomes are not very visible and appeared as chromatin. • The cell grows larger. • If the environmental condition is flavourable, the cell will decide to proceed to cell division. • The centrosome duplication process starts. Left: Fluorescence microscopic images of nuclei and chromosomes of BY-2 cells 染色质 中心体
  8. 8. S phase • Synthesis of DNA occurs in this phase. • DNA is replicated and each chromosome contain two identical sister chromatids that are joined together by a centromere.
  9. 9. G2 phase • The cell continue to grow in the second gap phase. • Organelles are synthesis and metabolism is active. • The DNA are present as chromatin. • The pair of centrosomes has matured. Fluorescence microscopic images of nuclei and chromosomes of BY-2 cells
  10. 10. Cell division 细胞分裂 • Cell division is the process of forming of new cell(s) from pre-existing cell. • Cell division can be achieved by the process of mitosis or meiosis, followed by cytokinesis. • Mitosis is the division of the cell nucleus which results in the production of two identical daughter nuclei. • Meiosis is a the division of the cell nucleus which results in the production of four unidentical daughter nuclei with half of the chromosome number of the parent cell. • Cytokinesis is the division of the cytoplasm into two. 有丝分裂 减数分裂 胞质分裂 细胞质
  11. 11. 5.1 Mitosis
  12. 12. Significance of mitosis 有丝分裂 • Increase number of cells for growth • Replacing dead or worn out cells, such as blood cells, epithelial cells • Repair injured organs and regenerate lost parts, such as tail of a lizard • Asexual reproduction • Binary fission in Amoeba • Budding in yeast • Vegetative reproduction in plants using rhizomes, tubers and bulbs 无性繁殖
  13. 13. The M phase (mitosis and cytokinesis) • Mitosis can be subdivided into four continuous phases: prophase, metaphase, anaphase and telophase. • Following telophase, cytokinesis occurs.
  14. 14. Prophase • In the nucleus, chromosomes condense, appear shorter and thicker and are visible under the light microscope. • In the cytoplasm, spindle fibres begin to form from the centrioles. Each pair of centrioles migrates to the opposite site poles of the cell. • The chromatids are attached to the spindle fibres by their centromeres. • The nucleolus disappears and the nuclear membrane disintegrates at the end of prophase. 纺锤体 着丝粒 核仁 核膜 前期
  15. 15. Metaphase • Centromeres of all the chromosome are lined up on the metaphase plate. • The mitotic spindle is now fully formed. • Each sister chromatid is attached to a spindle fibre originated from opposite pole. 赤道板 中期
  16. 16. Anaphase • The two sister chromatids of each chromosome separate at the centrode. • The sister chromatids are pulled apart to the opposite poles by the shortening of the spindle fibres. • Once separated, the chromatids are referred as daughter chromosomes. • By the end of anaphase, two poles of the cell have complete and equivalent set of chromosomes. 后期 姐妹染色单体
  17. 17. Telophase • The chromosomes uncoil and revert back to extended chromatin. • The chromosomes become less visible under the microscope. • The spindle fibres disappear. • New nuclear membrane forms. • Nucleolus re-forms in each nucleus. 末期
  18. 18. Cytokinesis in animal • In animal cell, actin filaments in the cytoplasm contracts to pull a ring of the plasma membrane inwards, forming a groove called a cleavage furrow. • Eventually the cell breaks at the constricted region and two daughter cells are form. 胞质分裂 槽 卵裂沟
  19. 19. Cytokinesis in plant • In the plant cells, vesicles gather at a plant cells equator to form a cell plate. • The cell plate grow until it fuses to from new cell walls and plasma membrane. 胞质分裂 细胞板
  20. 20. Mitosis Summary
  21. 21. Comparison of mitosis in plant and animal • Similarities • Involves interphase, prophase, metaphase, anaphase, telophase, cytokinesis • Nucleus divides once and cytoplasm divide once • Daughter cells are genetically identical to the parent cells. • Differences Animal cell Plant cell Spindle threads emerge from centrioles. Spindle threads do not emerge from centrioles. Cytokinesis occurs by constriction of the cytoplasm – cleavage furrow is formed. Cytokinesis occurs by the formation of cell plate.
  22. 22. Importance of controlled mitosis • Correct number of chromosomes is obtained by the daughter cell • Correct growth, development and maintenance of tissues • To avoid presence of cancerous cells that divide uncontrollably and form tumour Left: Atomic-force microscopy (AFM) maps of adhesion of the AFM probe to the cell surface of (a) normal, (b) immortal (premalignant), and (c) cancer cells. SEM images of (d) normal, (e) immortal, and (f) cancer cells. AFM provided a higher 3D resolution compared to SEM. [Sokolov et al, New Journal of Physics] Top, Spectral karyogram of normal human male chromosomes. Image by Nallasivam Palanisamy, Ph.D., Michigan Center for Translational Pathology. Bottom, Spectral karyogram of a breast cancer cell line. Image by Mira Grigorova and Paul Edwards
  23. 23. Application of mitosis: cloning • Cloning is the process of producing genetically identical organisms through asexual reproducing, such as budding, binary fission, grafting, stem cuttings and tissue culture. • Tissue culture is the growth of tissues and cells in sterile culture medium. • Plant cells will form undifferentiated callus, but later can developed into embryo, plantlets and adult plant. • Genetic engendering can altered the genes of the plant to enhance crop performance. 组织培养 愈合组织 胎 苗
  24. 24. Application of mitosis: animal cloning • Animal cloning involves the transfer of the nucleus from a somatic cell to an ovum or embryonic cell with the nucleus removed.
  25. 25. 5.2 Meiosis
  26. 26. Meiosis 减数分裂 • Meiosis is a type of cell division that reduces the number of chromosomes in the parent cell by half and produces four gamete cells. • This process is required to produce egg and sperm cells for sexual reproduction. • Sexual reproduction involves the fusion of two haploid gametes (n) during fertilization to produce a diploid zygote (2n). • Meiosis is divided into meiosis I and meiosis II. 二倍体 单倍体 有性生殖
  27. 27. Meiosis I • Meiosis I takes place after the interphase. • Here, gene recombination occurs here to generate diversity in the offspring. • The chromosomal number is reduced in the daughter cells produced in meiosis I.
  28. 28. Prophase I • The chromosomes condensed. • The homologous chromosomes come together to form bivalents (tetrads) through a process called synapsis. • Non-sister chromatids exchange segments of DNA in a process called crossing over. • The point at which the chromatids cross over is called chiasmata. • At the end of prophase I, the nucleolus and nuclear membrane disappear, centrioles migrate to the opposite poles of the cell and spindle fibre form. 交點 「二價體」或「四分體」聯會 染色體的交換 前期 I
  29. 29. Crossing over of homologous chromosome 同源染色体联会
  30. 30. Metaphase I • The chromosome are lined up side by side as tetrads on the metaphase plate. • Each tetrad is attached with two spindle fibre from the opposite pole. • The centromere does not divide. 中期 I
  31. 31. Anaphase I • The spindle fibres pull the homologous chromosome away. • Each chromosome still consists of two sister chromatids. 后期 I
  32. 32. Telophase I • Each pole has a haploid daughter nucleus because it contains only one set of chromosome. • The spindle fibres dissapear. • The nuclear membrane and nucleolus reappear. • Cytokinesis usually occurs simultaneously with telophase I. 末期 I
  33. 33. Meiosis II • Meiosis II generally occurs immediately after cytokinesis, usually with no interphase between them. • The chromatids still have two sister chromatids. • In meiosis II, the sister chromatids will be separated.
  34. 34. Prophase II • Chromosome condensed. • The nuclear membranes disintegrate. • Spindle fibres reformed. 前期 II
  35. 35. Metaphase II • The chromosome are rearranged in the metaphase plate with the sister chromatids of each chromosome pointing towards the opposite poles. • Each sister chromatid is attached to the spindle fibres at the centromere. 中期 II
  36. 36. Anaphase II • The centromeres of the sister chromatids separate. • The sister chromatids become individual chromosome. • The chromosomes movet owards the opposite poles of the cell. 后期 II
  37. 37. Telophase II • Nucleolus and nuclear membrane reform. • Spindle fibre break down. • Cytokinesis occurs after telophase II. • The daughter cells are haploid. 末期 II
  38. 38. Meiosis I summary The cells are haploid.
  39. 39. Meiosis II summary
  40. 40. Comparison between mitosis and meiosis Mitosis Meiosis One nuclear division Two nuclear division Two diploid daughter cell Four haploid daughter cell Daughter cells identical to parent cell Daughter cells unlike parent cell No genetic variation in daughter cells Genetic variation in daughter cells
  41. 41. 5.3 Appreciating the movement of chromosomes during mitosis and meiosis
  42. 42. Mutation • Mutation is the permanent alteration of the nucleotide sequence of the genome of an organism, virus, or extrachromosomal DNA or other genetic elements. • Radiation, carcinogenic chemicals such as nicotine, and food preservations (sodium nitrite 亚硝酸钠, benzene 苯, formaldehyde 甲醛) are known to cause changes to the DNA molecule or disturb mitosis and meiosis. • Mitosis and meiosis gone awry can lead to mutation. 突变 致癌
  43. 43. Down’s Syndrome • Down syndrome is usually caused by an error in cell division called "nondisjunction." • Nondisjunction is the failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during anaphase I or II. • Nondisjunction results in an embryo with three copies of chromosome 21 instead of the usual two. • Characteristic of affected individuals have slanted eyes, short stature and mental retardation. 染色体不分离 唐氏综合症
  44. 44. Summary • Two main phrases in the cell cycle is: • Interphase – cell grows and prepares for cell division • Cell division (M phase) – cell divides its nucleus and cytoplasm • Mitosis is the division of the cell nucleus which results in the production of two identical daughter nuclei. • Meiosis is a the division of the cell nucleus which results in the production of four unidentical daughter nuclei with half of the chromosome number of the parent cell. • Down’s syndrome is usually caused by an error in meiosis. Characteristic of affected individuals have slanted eyes, short stature and mental retardation.

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