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Cell Division

Cell Division. I. Cellular Growth ( ch 9-1). A. Why do cells need to divide? 1. Growth 2. Repair. repair. growth. B. Cell Cycle The cell cycle shows the different phases that a cell will complete during division There are 3 broad steps in the cell cycle 1. Interphase 2. M phase

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Cell Division

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  1. Cell Division

  2. I. Cellular Growth (ch 9-1) • A. Why do cells need to divide? • 1. Growth • 2. Repair repair growth

  3. B. Cell Cycle • The cell cycle shows the different phases that a cell will complete during division • There are 3 broad steps in the cell cycle • 1. Interphase • 2. M phase • 3. Cytokinesis

  4. 1. Interphase • Makes up the majority of the cell cycle • Comprised of 3 phases • 1. G1 • 2. S • 3. G2

  5. 2. M (mitosis) phase • This involves the division of the nucleus and chromosomes • The majority of the details and information takes place during the M phase • Phases include • 1. prophase • 2. metaphase • 3. anaphase • 4. telophase

  6. 3. Cytokinesis • The actual division of the cytoplasm

  7. II. Chromosomes • A. Definition • Chromosomes are found in the nucleus and contain DNA • DNA: holds the genetic information (hair color, etc)

  8. B. Chromosome Structure • Chromosomes are commonly comprised of 2 chromatids • These chromatids are usually called sister chromatids • Chromatids are held together by a centromere • Chromatids are comprised of chromatin • Chromatin is comprised of DNA wrapped around histones (proteins)

  9. C. Chromosome Number • There are 46 individual chromosomes (23 pairs) found in each human body cell • Every cell that has 23 pairs is a called a diploid cell

  10. There are 44 autosomes (22 pairs) • These autosomes are called body chromosomes and hold the info for the majority of the human body • There are 2 sex chromosomes (1 pair) • These sex chromosomes determine if the person is a male or female

  11. D. Karyotype • A picture of your chromosomes • The picture is taken during metaphase

  12. III. Phases of Mitosis

  13. Interphase G1 Immediately after cell divides Cell grows & performs normal functions S DNA replication G2 Cell prepares to divide Protein for microtubules formed

  14. Prophase Nuclear membrane breaks down Chromatin condenses to form chromosomes Nucleolus disappears Spindle apparatus formed

  15. Metaphase Spindle fibers connect to chromosomes Chromosomes line up along center of cell Ensures each new cell gets a complete copy of DNA

  16. Anaphase Spindle fibers shorten, pulling at centromere Sister chromatids separate into identical chromosomes Chromosomes travel to alternate poles of the cell

  17. Telophase Chromosomes reach the poles Chromosomes relaxes into chromatin Nuclear membrane forms Nucleolus forms Spindle fibers breakdown

  18. Cytokinesis Cytoplasm divides 2 cells with 2 identical nuclei Animal Cells Microfilaments Cleavage Furrow Plant Cells Cell Plate Cell walls form

  19. IV. Meiosis • Meiosis is the making of gametes • Egg and sperm

  20. Mitosis vs Meiosis Mitosis Meiosis • 1. 1 cell becomes 2 cell • 2. Daughter cells are genetically identical • 3. Only occurs in body cells • 4. involves one set of cell division • 5. Diploid to diploid (46  46) • 1. 1 cell becomes 4 cells • 2. Daughter cells are genetically different • 3. Only occurs in reproductive cells • 4. Involves two sets of cell division • 5. Diploid to haploid (46  23)

  21. Terms • 1. Diploid: 2 sets of chromosomes • one from mom, one from dad • 46 chromosomes in humans • 2. Haploid: 1 set of chromosomes • Results from meiosis • 23 chromosomes

  22. Homologous Chromosomes • Refers to chromosomes that are the same • There are 23 pairs of homologous chromosomes in a human • Once again, one from your mom, one from your dad

  23. Fertilization • The union of egg and sperm to form a zygote • Haploid sperm + haploid egg  diploid zygote • 23 + 23 = 46 chromosomes

  24. Steps of Meiosis: Meiosis I • A. Interphase • Same as interphase of mitosis • G1 • S • G2

  25. B. Prophase I • By far the most “stuff” happens during this phase • 1. Synapsis occurs • This is the pairing of homologous chromosomes • Results in a tetrad • Homologous pair • Tetrad refers to the 4 chromatids in the pair

  26. Prophase I • 2. Crossing Over • This is when the homologous chromosomes literally cross over each other and exchange pieces of DNA • Results in genetic variation: this is a HUGE for evolution

  27. Prophase I • 3. all of the other “normal” stuff during prophase of mitosis • Nuclear membrane/envelope breaks down • Chromatin condenses into chromosomes • Spindle apparatus appears

  28. C. Metaphase I • Homologous PAIRS line up along the middle of the cell • Independent assortment takes place • Search video of independent assortment later • Leads to more genetic variation • Also HUGE for evolution

  29. D. Anaphase I • Homologous PAIRS separate

  30. E. Telophase I • PAIRS each opposite sides of cell

  31. F. SKIP interphase • There is no DNA replication

  32. Meiosis II • This is almost the same as regular mitosis

  33. G. Prophase II (same as mitosis) • Nuclear membrane breaks down • Chromosomes become visible (chromatin condenses) • Spindle apparatus forms

  34. H. Metaphase II (same as mitosis) • Individual chromosomes line up along the middle of the cell

  35. I. Anaphase II (same as mitosis) • Sister chromatids separate

  36. J. Telophase II (same as mitosis) • Chromatids (now officially called chromosomes) reach opposites ends of the cell

  37. K. Cytokinesis • The division of the cytoplasm

  38. IV. Meiosis in Males vs Females • A. Spermatogensis (males) • This is meiosis that results in 4 haploid cells called sperm • The 4 sperm are normal, functioning sex cells

  39. B. Oogenesis (females) • Results in 4 haploid cells • However, 1 is called the egg, the other 3 cells are called polar bodies • Polar bodies will break down and disappear • Uneven division of the cytoplasm • The one egg gets lots of cytoplasm, the 3 polar bodies will get very little cytoplasm

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