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Mitosis and Meiosis

Mitosis and Meiosis. The Role of Mitosis. Two Stages -Divide nucleus & DNA -Divide cell (cytokinesis) Purpose: to produce 2 identical cells for… -Growth -Repair of tissue -Replace dead cells -Asexual Reproduction. Terms to know!.

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Mitosis and Meiosis

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  1. Mitosis and Meiosis

  2. The Role of Mitosis • Two Stages -Divide nucleus & DNA -Divide cell (cytokinesis) • Purpose: to produce 2 identical cells for… -Growth -Repair of tissue -Replace dead cells -Asexual Reproduction

  3. Terms to know! • DIPLOID (2n): Full complement of chromosomes. • In humans 2n = 46 • HAPLOID (n): Number of unique chromosomes • In humans n = 23

  4. Diploid or Haploid? In a cabbage cell the Diploid number is 2n = 18 What is the Haploid number? n = 9 How many homologous pairs? 9

  5. The Cell Cycle • See page 122 • Most of the cell’s time is spent in Interphase!

  6. Stages of Mitosis - Interphase • This is the parent cell • Rapid growth • Cell doing its job • DNA replication (chromatin) • Prepares for division

  7. Stages of Mitosis - Prophase • DNA condenses into chromatids – Dyads form. • Nuclear membrane disappears • Spindle fibers form from centrioles and attach to centromeres.

  8. Stages of Mitosis - Metaphase • Dyads line up down the middle. • Pulled into place by spindle fibres.

  9. Stages of Mitosis - Anaphase • Dyads are pulled apart (by spindle fibers) to form monads

  10. Stages of Mitosis - Telophase • Nuclear membrane reforms • Cytokinesis occurs (cell divides) • 2 identical daughter cells (DIPLOID – 2n)

  11. Mitosis in Plant Cells • No centrioles • A cell plate forms, then cell wall.

  12. Meiosis and Variation • Variation is key for species survival, allows organisms to adapt! • During Meiosis, two events occur which increase variation…

  13. Independent (Random) Assortment • When tetrads line up at Metaphase I, the paternal and maternal chromosomes line up randomly on the left and right. • 223 = 8 388 608 different combinations!

  14. Crossing Over • While the dyads are in the tetrad, pieces of homologous chromatids can change places, creating different chromosomes. • This is desirable and occurs frequently • If one piece gets misplaced, a mutation occurs (genes are missing)

  15. Stages of Meiosis • Use your textbook (Pg. 134-135) and the handout to document the steps in Meiosis

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