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Meiosis

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Meiosis

  1. 1. MEIOSIS The significance of meiosis
  2. 2. Meiosis <ul><li>Cell division that is vital for sexual reproduction </li></ul><ul><li>Takes place in reproductive organs </li></ul><ul><li>Results in formation of haploid gametes </li></ul><ul><li>The four daughter cells are not genetically identical </li></ul>
  3. 3. Meiosis and genetic variation <ul><li>There are two main ways in which genetic </li></ul><ul><li>variation occurs at meiosis: </li></ul><ul><li>Random segregation of chromosomes </li></ul><ul><li>Crossing over </li></ul>
  4. 4. Meiosis and genetic variation <ul><li>Random segregation </li></ul><ul><li>During metaphase 1 homologous chromosomes arrive at the equator </li></ul><ul><li>They arrange themselves in a random order on the equator </li></ul>
  5. 5. Meiosis and genetic variation <ul><li>Random segregation </li></ul><ul><li>In a cell with just two pairs of chromosomes there are four different types of outcomes for the way the chromosomes can separate. </li></ul>
  6. 6. Meiosis and genetic variation <ul><li>Random segregation </li></ul><ul><li>In human cells with 23 chromosomes there are 2 23 different possible ways the chromosomes can segregate! </li></ul><ul><li>That is over 8 000 000 different types of gamete </li></ul>
  7. 7. Meiosis and genetic variation <ul><li>During fertilization any male gamete can join with any female gametes. </li></ul><ul><li>So thousands of millions of new genetic combinations are possible. </li></ul>
  8. 8. Meiosis and genetic variation <ul><li>Crossing over </li></ul><ul><li>During prophase 1 of meiosis homologous chromosomes come together in pairs </li></ul>
  9. 9. Meiosis and genetic variation <ul><li>Crossing over </li></ul><ul><li>Each chromosome is divided into two chromatids </li></ul><ul><li>The homologous chromosomes twist around each other </li></ul><ul><li>This creates tension, which may cause breaks to occur along the length of the chromatids </li></ul>
  10. 10. Meiosis and genetic variation <ul><li>Crossing over </li></ul><ul><li>During cross over, corresponding fragments may get swapped over. </li></ul><ul><li>This “cutting and sticking” means that genetic material is exchanged. </li></ul><ul><li>This creates new genetic combinations and variation in the gametes is increased. </li></ul>
  11. 12. Differences between mitosis and meiosis <ul><li>Mitosis Meiosis </li></ul><ul><li>one division </li></ul>
  12. 13. Differences between mitosis and meiosis <ul><li>Mitosis Meiosis </li></ul><ul><li>one division two divisions </li></ul>
  13. 14. Differences between mitosis and meiosis <ul><li>Mitosis Meiosis </li></ul><ul><li>one division two divisions </li></ul><ul><li>the number of chromosomes </li></ul><ul><li>remains the same </li></ul>
  14. 15. Differences between mitosis and meiosis <ul><li>Mitosis Meiosis </li></ul><ul><li>one division two divisions </li></ul><ul><li>the number of chromosomes the number of </li></ul><ul><li>remains the same chromosomes is halved </li></ul>
  15. 16. Differences between mitosis and meiosis <ul><li>Mitosis Meiosis </li></ul><ul><li>one division two divisions </li></ul><ul><li>the number of chromosomes the number of </li></ul><ul><li>remains the same chromosomes is halved </li></ul><ul><li>homologous chromosomes </li></ul><ul><li>do not pair up </li></ul>
  16. 17. Differences between mitosis and meiosis <ul><li>Mitosis Meiosis </li></ul><ul><li>one division two divisions </li></ul><ul><li>the number of chromosomes the number of </li></ul><ul><li>remains the same chromosomes is halved </li></ul><ul><li>homologous chromosomes homologous chromosomes </li></ul><ul><li>do not pair up pair up to form bivalents </li></ul>
  17. 18. Differences between mitosis and meiosis <ul><li>Mitosis Meiosis </li></ul><ul><li>one division two divisions </li></ul><ul><li>the number of chromosomes the number of </li></ul><ul><li>remains the same chromosomes is halved </li></ul><ul><li>homologous chromosomes homologous chromosomes </li></ul><ul><li>do not pair up pair up to form bivalents </li></ul><ul><li>chiasmata do not form and </li></ul><ul><li>cross over never occurs </li></ul>
  18. 19. Differences between mitosis and meiosis <ul><li>Mitosis Meiosis </li></ul><ul><li>one division two divisions </li></ul><ul><li>the number of chromosomes the number of </li></ul><ul><li>remains the same chromosomes is halved </li></ul><ul><li>homologous chromosomes homologous chromosomes </li></ul><ul><li>do not pair up pair up to form bivalents </li></ul><ul><li>chiasmata do not form and chiasmata form and cross over </li></ul><ul><li>cross over never occurs occurs </li></ul>
  19. 20. Differences between mitosis and meiosis <ul><li>Mitosis Meiosis </li></ul><ul><li>one division two divisions </li></ul><ul><li>the number of chromosomes the number of </li></ul><ul><li>remains the same chromosomes is halved </li></ul><ul><li>homologous chromosomes homologous chromosomes </li></ul><ul><li>do not pair up pair up to form bivalents </li></ul><ul><li>chiasmata do not form and chiasmata form and cross over </li></ul><ul><li>cross over never occurs occurs </li></ul><ul><li>daughter cells are genetically </li></ul><ul><li>identical </li></ul>
  20. 21. Differences between mitosis and meiosis <ul><li>Mitosis Meiosis </li></ul><ul><li>one division two divisions </li></ul><ul><li>the number of chromosomes the number of </li></ul><ul><li>remains the same chromosomes is halved </li></ul><ul><li>homologous chromosomes homologous chromosomes </li></ul><ul><li>do not pair up pair up to form bivalents </li></ul><ul><li>chiasmata do not form and chiasmata form and cross over </li></ul><ul><li>cross over never occurs occurs </li></ul><ul><li>daughter cells are genetically daughter cells are genetically </li></ul><ul><li>identical different from the parent cells </li></ul>
  21. 22. Differences between mitosis and meiosis <ul><li>Mitosis Meiosis </li></ul><ul><li>one division two divisions </li></ul><ul><li>the number of chromosomes the number of </li></ul><ul><li>remains the same chromosomes is halved </li></ul><ul><li>homologous chromosomes homologous chromosomes </li></ul><ul><li>do not pair up pair up to form bivalents </li></ul><ul><li>chiasmata do not form and chiasmata form and cross over </li></ul><ul><li>cross over never occurs occurs </li></ul><ul><li>daughter cells are genetically daughter cells are genetically </li></ul><ul><li>identical different from the parent cells </li></ul><ul><li>two daughter cells are formed </li></ul>
  22. 23. Differences between mitosis and meiosis <ul><li>Mitosis Meiosis </li></ul><ul><li>one division two divisions </li></ul><ul><li>the number of chromosomes the number of </li></ul><ul><li>remains the same chromosomes is halved </li></ul><ul><li>homologous chromosomes homologous chromosomes </li></ul><ul><li>do not pair up pair up to form bivalents </li></ul><ul><li>chiasmata do not form and chiasmata form and cross over </li></ul><ul><li>cross over never occurs occurs </li></ul><ul><li>daughter cells are genetically daughter cells are genetically </li></ul><ul><li>identical different from the parent cells </li></ul><ul><li>two daughter cells are formed four daughter cells are formed </li></ul>

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