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CELL DIVISION

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  1. CELL DIVISION

  2. Cell Division • One cell  Two identical cells • Cells must be able to pass on ALL information from their DNA • So DNA must be replicated before cell division occurs

  3. Prokaryotic Cells • No nucleus • DNA is found as circular molecule • BINARY FISSION • DNA replicates • DNA attaches to membrane • Cell pinches & splits

  4. Eukaryotic Cells • Much more complicated • Chromosome – DNA coiled around proteins

  5. Formation of chromosomes • DNA at “rest” found unorganized in nucleus • Just before cell division, it organizes itself into chromosomes

  6. Human Chromosomes

  7. Parts of a Chromosome

  8. UNDERSTANDING CHECK

  9. How many do humans have? • Somatic cells = DIPLOID (2n) • 46 chromosomes (23 pairs) • 22 pairs = Autosomes • 1 pair = Sex chromosomes (X & Y) • XX (female) vs. XY (male)

  10. Human Karyotype

  11. Human Karyotype

  12. UNDERSTANDING CHECK

  13. Gametes = HAPLOID (n) Formed from germ cells 23 chromosomes (one of each) Sperm + Egg = Zygote  YOU! 23 + 23 = 46 How many do humans have?

  14. Haploid + Haploid = Diploid

  15. Cell Cycle

  16. Cell Cycle • G1 – 1st Growth – Routine functions • S – Synthesis – DNA Replication • G2 – 2nd Growth – Prepare to Divide • M – Mitosis – Division of the Nucleus • C – Cytokinesis – Division of the Cytoplasm • MOVIE

  17. UNDERSTANDING CHECK

  18. Cell Cycle • Numerous ways to control speed • Malfunction of cell cycle = cancer

  19. Interphase • Includes the G1, S, & G2 phases • When the cell is not dividing or “at rest” • DNA is found unorganized in the nucleus

  20. Interphase

  21. Mitosis • Division of the nucleus to form 2 identical nuclei • Chromosome = 2 identical chromatids (formed after replication)

  22. UNDERSTANDING CHECK

  23. Mitosis • Prophase • Metaphase • Anaphase • Telophase • MOVIE 1 • MOVIE 2

  24. Prophase • Chromosomes become visible • Nuclear envelope dissolves • Spindle forms from centrioles

  25. Prophase

  26. Metaphase • Chromosomes line up along equator

  27. Anaphase • Chromatids separate and reeled to opposite poles

  28. Telophase • Nuclear envelope forms at each pole • Chromosomes uncoil • Spindle dissolves • Cytokinesis begins

  29. Telophase

  30. UNDERSTANDING CHECK

  31. Cytokinesis • Division of the cytoplasm • Animal cells – pinch and split • Plant cells – forms cell plate down the center • MOVIE

  32. Meiosis • Formation of haploid gametes from one germ cell • Homologous chromosomes – chromosomes of similar size, shape, & genetic content

  33. Meiosis • Meiosis I • Prophase I • Metaphase I • Anaphase I • Telophase I • Meiosis II • Prophase II • Metaphase II • Anaphase II • Telophase II

  34. Prophase I • Homologous chromosomes pair up & crossing over occurs • Animation • Allows genetic variation

  35. Prophase I • Chromosomes become visible • Nuclear env. breaks down • Spindle forms • Crossing over

  36. Metaphase I • Pairs of homologous chromosomes move to equator of cell

  37. Anaphase I • Homologous chromosomes reeled to opposite poles

  38. Telophase I • Chromosomes gather at poles • Cytokinesis

  39. Prophase II • New spindle forms

  40. Metaphase II • Chromosomes line up on equator

  41. Anaphase II • Chromatids reeled to opposite poles

  42. Telophase II • Nuclear envelope forms • Cytokinesis

  43. Meiosis

  44. UNDERSTANDING CHECK

  45. What can go wrong? • Nondisjunction– the chromosomes fail to separate during meiosis • Trisomy – individual has 3 of a particular chromosome • Down syndrome = trisomy 21

  46. UNDERSTANDING CHECK

  47. Meiosis in Males

  48. Meiosis in Females

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