Mitosis%20and%20Meiosis

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Mitosis and Meiosis
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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

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Terms to know!

• DIPLOID (2n) Full complement of
  chromosomes.
• In humans 2n 46
• HAPLOID (n) Number of unique chromosomes
• In humans n 23

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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

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The Cell Cycle

• Most of the cells time is spent in Interphase!

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Stages of Mitosis - Interphase

• This is the parent cell
• Rapid growth
• Cell doing its job
• DNA replication (chromatin)
• Prepares for division

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Stages of Mitosis - Prophase

• DNA condenses into chromatids (thicker)
• Nuclear membrane disappears
• Spindle fibers form from centrioles and attach to
  centromeres.

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Stages of Mitosis - Metaphase

• Chromatids line up down the middle.
• Pulled into place by spindle fibres.

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Stages of Mitosis - Anaphase

• Chromatids are pulled apart (by spindle fibers)

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Stages of Mitosis - Telophase

• Nuclear membrane reforms
• Cytokinesis occurs (cell divides)
• 2 identical daughter cells (DIPLOID 2n)

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Mitosis in Plant Cells

• No centrioles
• A cell plate forms,
• then cell wall.

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Meiosis and Variation

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

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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!

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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)

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Stages of Meiosis

• Use your textbook (Pg. 154-155) and the handout
  to document the steps in Meiosis