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CHAPTER 9 Chromosomes, the Cell Cycle, and Cell Division

CHAPTER 9 Chromosomes, the Cell Cycle, and Cell Division. Chapter 9: Chromosomes, the Cell Cycle, and Cell Division. Systems of Cell Reproduction Interphase and the Control of Cell Division Eukaryotic Chromosomes Mitosis: Distributing Exact Copies of Genetic Information.

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CHAPTER 9 Chromosomes, the Cell Cycle, and Cell Division

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  1. CHAPTER 9Chromosomes, the Cell Cycle, and Cell Division

  2. Chapter 9: Chromosomes, the Cell Cycle, and Cell Division Systems of Cell Reproduction Interphase and the Control of Cell Division Eukaryotic Chromosomes Mitosis: Distributing Exact Copies of Genetic Information

  3. Chapter 9: Chromosomes, the Cell Cycle, and Cell Division Cytokinesis: The Division of the Cytoplasm Reproduction: Sexual and Asexual Meiosis: A Pair of Nuclear Divisions Meiotic Errors Cell Death

  4. Cell Division • Cell division is necessary for reproduction, growth, and repair of an organism. 4

  5. Systems of Cell Reproduction • Cell division must be initiated by a reproductive signal and consists of three steps: • replication of the genetic material (DNA) • partitioning of the two DNA molecules • division of the cytoplasm 5

  6. Systems of Cell Reproduction • In prokaryotes, cellular DNA is a single molecule, or chromosome. • Prokaryotes reproduce by cell fission. Review Figure 9.3 6

  7. figure 09-03.jpg Figure 9.3 Figure 9.3

  8. Systems of Cell Reproduction • In eukaryotes, nuclei divide by either mitosis or meiosis. 8

  9. Interphase and the Control of Cell Division • The mitotic cell cycle has two main phases: interphase and mitosis. 9

  10. Interphase and the Control of Cell Division • During most of the cell cycle the cell is in interphase, which is divided into three subphases: S, G1, and G2. • DNA is replicated during S phase. Review Figure 9.4 10

  11. figure 09-04.jpg Figure 9.4 Figure 9.4

  12. Interphase and the Control of Cell Division • Cyclin-Cdk complexes regulate the passage of cells from G1 into S phase and from G2 into M phase. Review Figure 9.5 12

  13. figure 09-05.jpg Figure 9.5 Figure 9.5

  14. Interphase and the Control of Cell Division • In addition to the internal cyclin-Cdk complexes, controls external to the cell, such as growth factors and hormones, can also stimulate a division cycle. 14

  15. Eukaryotic Chromosomes • Chromosomes contain DNA and proteins. • At mitosis, chromosomes initially appear double because two sister chromatids are held together at the centromere. • Each sister chromatid consists of one double-stranded DNA molecule complexed with proteins and referred to as chromatin. 15

  16. Eukaryotic Chromosomes • During interphase, DNA in chromatin is wound around histone cores to form nucleosomes. • DNA folds repeatedly, packing within the nucleus. When mitotic chromosomes form, it folds even more. Review Figure 9.7 16

  17. figure 09-07.jpg Figure 9.7 Figure 9.7

  18. Mitosis: Distributing Exact Copies of Genetic Information • After DNA is replicated during S phase, the first sign of mitosis is the separation of centrosomes, which initiate microtubule formation for the spindle. Review Figure 9.9 18

  19. figure 09-09.jpg Figure 9.9 Figure 9.9

  20. Mitosis: Distributing Exact Copies of Genetic Information • Mitosis can be divided into phases: • prophase • metaphase • anaphase • telophase Review Figure 9.8 20

  21. figure 09-08a.jpg Figure 9.8 – Part 1 Figure 9.8 – Part 1

  22. figure 09-08b.jpg Figure 9.8 – Part 2 Figure 9.8 – Part 2

  23. Mitosis: Distributing Exact Copies of Genetic Information • During prophase, the chromosomes condense and appear as paired chromatids. • Centrioles move to the poles. • Spindle fibers form. • Chromosomes move toward the middle of the cell. 23

  24. Mitosis: Distributing Exact Copies of Genetic Information • In Metaphase, chromosomes line up on the equator and their centromeres attach to a spindle fiber. • At Anaphase, chromatid pairs separate and migrates to opposite poles. 24

  25. Mitosis: Distributing Exact Copies of Genetic Information • During telophase, the chromosomes uncoil. • The nuclear membranes re-form, producing two nuclei identical to each other and the original cell. • The cytoplasm then divides. Review Figure 9.8 25

  26. Cytokinesis: The Division of the Cytoplasm • Cytokinesis usually follows nuclear division. • Animal cells pinch in to divide cytoplasm. • In plant a new cell wall is built. 26

  27. Reproduction: Sexual and Asexual • Asexual reproduction produces an organism genetically identical to the parent. • Any genetic variety is the result of mutations. 28

  28. Reproduction: Sexual and Asexual • In sexual reproduction, two haploid gametes—one from each parent—unite in fertilization to form a genetically unique, diploid zygote. Review Figure 9.12 29

  29. figure 09-12a.jpg Figure 9.12 – Part 1 Figure 9.12 – Part 1

  30. figure 09-12b.jpg Figure 9.12 – Part 2 Figure 9.12 – Part 2

  31. figure 09-12c.jpg Figure 9.12 – Part 3 Figure 9.12 – Part 3

  32. Reproduction: Sexual and Asexual • In sexually reproducing organisms, certain cells in the adult undergo meiosis, whereby a diploid cell produces haploid gametes. • Each gamete contains a random mix of one of each pair of homologous chromosomes from the parent. 33

  33. Reproduction: Sexual and Asexual • The number, shapes, and sizes of the chromosomes constitute the karyotype of an organism. 34

  34. Meiosis: A Pair of Nuclear Divisions • Meiosis reduces the chromosome number from diploid to haploid and ensures that each haploid cell contains one member of each chromosome pair. • It consists of two nuclear divisions. Review Figure 9.14 35

  35. figure 09-14a.jpg Figure 9.14 – Part 1 Figure 9.14 – Part 1

  36. figure 09-14b.jpg Figure 9.14 – Part 2 Figure 9.14 – Part 2

  37. Meiosis: A Pair of Nuclear Divisions • During prophase I homologous chromosomes pair, and crossing over occurs between homologs. • In metaphase I, the paired homologs line up at the equatorial. • Both chromosomes attach to the same spindle fiber. • In anaphase I, chromosome pairs split and move to the poles. • After Telophase I, there are two haploid cells. Review Figures 9.14, 9.16 38

  38. figure 09-16.jpg Figure 9.16 Figure 9.16

  39. Meiosis: A Pair of Nuclear Divisions • In meiosis II, the sister chromatids separate. • No DNA replication precedes this division. • The result of meiosis is four haploid cells. Review Figures 9.14, 9.17 40

  40. figure 09-17a.jpg Figure 9.17 – Part 1 Figure 9.17 – Part 1

  41. figure 09-17b.jpg Figure 9.17 – Part 2 Figure 9.17 – Part 2

  42. Meiosis: A Pair of Nuclear Divisions • Both crossing over and the independent assortment of chromosomes ensure that the genetic composition of gametes is different from that of the parent and other gametes. 43

  43. Meiotic Errors • In non-disjunction, one member of a homologous pair of chromosomes fails to separate from the other, and both go to the same pole. • Fertilization with a normal haploid gamete results in aneuploidy and genetic abnormalities that are invariably harmful or lethal. Review Figure 9.18 44

  44. figure 09-18.jpg Figure 9.18 Figure 9.18

  45. Cell Death • Cells may die by necrosis or may self-destruct by apoptosis, a genetically programmed series of events that includes the detachment of the cell from its neighbors and the fragmentation of its nuclear DNA. Review Figure 9.19 46

  46. figure 09-19.jpg Figure 9.19 Figure 9.19

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