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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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Presentation Transcript
the role of mitosis
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
Terms to know!
  • DIPLOID (2n): Full complement of chromosomes.
  • In humans 2n = 46
  • HAPLOID (n): Number of unique chromosomes
  • In humans n = 23
diploid or haploid
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

the cell cycle
The Cell Cycle
  • See page 122
  • Most of the cell’s time is spent in Interphase!
stages of mitosis interphase
Stages of Mitosis - Interphase
  • This is the parent cell
  • Rapid growth
  • Cell doing its job
  • DNA replication (chromatin)
  • Prepares for division
stages of mitosis prophase
Stages of Mitosis - Prophase
  • DNA condenses into chromatids – Dyads form.
  • Nuclear membrane disappears
  • Spindle fibers form from centrioles and attach to centromeres.
stages of mitosis metaphase
Stages of Mitosis - Metaphase
  • Dyads line up down the middle.
  • Pulled into place by spindle fibres.
stages of mitosis anaphase
Stages of Mitosis - Anaphase
  • Dyads are pulled apart (by spindle fibers) to form monads
stages of mitosis telophase
Stages of Mitosis - Telophase
  • Nuclear membrane reforms
  • Cytokinesis occurs (cell divides)
  • 2 identical daughter cells (DIPLOID – 2n)
mitosis in plant cells
Mitosis in Plant Cells
  • No centrioles
  • A cell plate forms,

then cell wall.

meiosis and variation
Meiosis and Variation
  • Variation is key for species survival, allows organisms to adapt!
  • During Meiosis, two events occur which increase variation…
independent random assortment
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!
crossing over
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)
stages of meiosis
Stages of Meiosis
  • Use your textbook (Pg. 134-135) and the handout to document the steps in Meiosis