Meosis and mitosis
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Meosis and mitosis

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Meosis and mitosis Presentation Transcript

  • 1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 10 Lecture Slides To run the animations you must be in Slideshow View. Use the buttons on the animation to play, pause, and turn audio/text on or off. Please Note: Once you have used any of the animation functions (such as Play or Pause), you must first click in the white background before you can advance to the next slide.
  • 2. 10.1 Discovery of Meiosis • Gametes are reproductive cells (eggs and sperm) that contain half the complement of chromosomes found in somatic cells  the gametes fuse to form a new cell called a zygote, which contains two complete copies of each chromosome • the fusion of gametes is called fertilization, or syngamy
  • 3. 10.1 Meiosis • The formation of gametes must involve some mechanism to halve the number of chromosomes found in somatic cells  if not the number of chromosomes would double with each fertilization  meiosis is a process of reduction division in forming gametes • this ensures a consistent chromosome number across generations
  • 4. 10.1 Discovery of Meiosis • Meiosis and fertilization constitute a cycle of sexual reproduction • Somatic cells have two sets of chromosomes making them diploid • Gametes have only one set of chromosomes, making them haploid Figure 10.1 Diploid cells carry chromosomes from two parents
  • 5. 10.1 Discovery of Meiosis • Some organisms reproduce by mitotic division and do not involve gametes  this is called asexual reproduction  an example is binary fission in prokaryotes • Other organisms are able to reproduce both sexually and asexually  for example, strawberry plants flower (sexual reproduction) and send out runners (asexual reproduction)
  • 6. 10.2 The Sexual Life Cycle • In sexual reproduction, haploid cells or organisms alternate with diploid cells or organisms Figure 10.3 Three types of sexual life cycles
  • 7. 10.2 The Sexual Life Cycle • In animals, the cells that will eventually undergo meiosis are reserved early on for the purpose of reproduction  these cells are referred to as germ-line cells and are diploid like somatic cells  but only the germ-line cells will undergo meiosis to produce haploid gametes
  • 8. Figure 10.4 The sexual life cycle in animals
  • 9. 10.3 The Stages of Meiosis • Meiosis involves two divisions, meiosis I and meiosis II  meiosis I separates the homologues in a homologous pair  DNA is replicated only before meiosis I  meiosis II separates the replicate sister chromatids  when meiosis is complete, the result is that one diploid cell has become four haploid cells
  • 10. Figure 10.7 How meiosis works
  • 11. Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • 12. 10.3 The Stages of Meiosis • Meiosis I is traditionally divided into four sequential stages 1. Prophase I • Homologues pair up and exchange segments 1. Metaphase I • The paired homologous chromosomes align on a central plane 1. Anaphase I • Homologues separate from the pairing and move to opposite poles 1. Telophase I • Individual chromosomes gather at each of the two poles
  • 13. 10.3 The Stages of Meiosis • During prophase I, homologous chromosomes line up together as a pair  crossing over occurs between two nonsister chromatids of homologous chromosomes • the chromatids break in the same place, and sections of chromosomes are swapped • the result is a hybrid chromosome  the pairing is held together by the cohesion between sister chromatids and the crossovers
  • 14. Figure 10.5 Crossing over
  • 15. 10.3 The Stages of Meiosis • During metaphase I, the orientation of the homologous chromosome pairs is a matter of chance  each possible orientation of which homologue in a homologous pair faces which pole results in gametes with different combinations of parental chromosomes  this process is called independent assortment
  • 16. Figure 10.6 Independent assortment
  • 17. Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • 18. 10.3 The Stages of Meiosis • In anaphase I, the chromosome pairs separate and individual homologues move to each pole • In telophase I, the chromosomes gather at their respective poles to form two chromosome clusters
  • 19. Figure 10.8 Meiosis (just Meiosis I)
  • 20. 10.3 The Stages of Meiosis • After meiosis I, a brief interphase occurs where there is no replication of DNA • Meiosis II follows and is basically a mitotic division of the products of meiosis I  except that the sister chromatids are non- identical because of crossing over in meiosis I
  • 21. 10.3 The Stages of Meiosis • Meiosis II is also divided into four stages 1. Prophase II • new spindle forms to attach to chromosome clusters 1. Metaphase II • spindle fibers bind to both sides of the centromere and individual chromosomes align along a central plane 1. Anaphase II • sister chromatids move to opposite poles 1. Telophase II • the nuclear envelope is reformed around each of the four sets of daughter chromosomes
  • 22. Figure 10.8 Meiosis (Meiosis II only)
  • 23. Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • 24. 10.4 How Meiosis Differs from Mitosis • Meiosis has two unique features not found in mitosis  synapsis • this is the process of drawing together homologous chromosomes down their entire lengths so that crossing over can occur  reduction division • because meiosis involves two nuclear divisions but only one replication of DNA, the final amount of genetic material passed to the gametes is halved
  • 25. Figure 10.9 Unique features of meiosis
  • 26. Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • 27. Figure 10.10 A comparison of meiosis and mitosis
  • 28. Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • 29. 10.5 Evolutionary Consequences of Sex • Sexual reproduction has an enormous impact on how species evolve because it rapidly generates new genetic combinations • Three mechanisms help produce this variety 1. Independent assortment 2. Crossing over 3. Random fertilization
  • 30. Inquiry & Analysis • Is there a difference in the rate at which microtubules are synthesized during interphase and metaphase? • When are the microtubules of the spindle assembled? Are New Microtubules Made During Cell Division?