The Cell Cycle, Mitosis and Meiosis

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The Cell Cycle, Mitosis and Meiosis

• Cell Reproduction

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The Cell Cycle
Most of a cells time not spent dividing
G 1 Gap 1 or Growth1 cell is growing after
just being created
S stands for Synthesis. DNA is copied before the
cell can divide again
G2 is a second growth stage as the cell prepares
to divide again
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Mitosis is used to.

• Mitosis is used for asexual reproduction. To
  spread out in a habitat by making clones.
• It is also used to grow and develop and repair
  injuries

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This is a clone of Aspen Trees. They are all
genetically identical
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There are 4 Steps to Mitosis, and Interphase when
cells are in the G, S and G2 parts of the cell
cycle
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During the S part of the Cell cycle, the DNA
Replicates
This creates two identical pieces of DNA
called sister chromatids
Together the two sisters Make up a chromosome
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Prophase (First phase) Occurs as the chromosomes
become visible and the nuclear membrane begins
to break down.
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During Metaphase (middle phase) The
Chromosomes Line up in the middle of The cell.
Having been Pushed and pulled on By the spindle
fibers
Spindle Fibers
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Each sister chromatid attaches to different
spindle fibers at the Kinetochores of the
chromatids
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During Anaphase (Separate) The spindle fibers
shorten, pulling the sister chromatids apart to
opposite ends of the cell. Once apart they are
now each called Chromosomes.
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Telophase (End phase) Two nuclei reform, and a
new cell wall called a cell plate is built in
plants to separate the cytoplasm of the two new
daughter cells.
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The two daughter cells are identical to each
other and to the parent cell which created them
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Mitosis works fine for
Growth and development
Repair of damaged tissue
But it cant be used to make egg or sperm cells
because
Egg and sperm cells (gametes) need one half the
chromosomes of the parent cell
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Meiosis

• Sexual Reproduction in Plants
• Meiosis makes cells with 1/2 of the chromosomes
  as the parent cell.
• In plants this process makes either male
  microspores that become sperm, or female
  megaspores that become eggs

This process also makes unique cells
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In plants a diploid (two sets of Chromosomes)
generation Does meiosis to make a haploid (half
the number of Chromosomes) generation.
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Homologous Chromosomes Pairs of chromosomes that
control the same traits
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• During Meiosis the cell goes through two divisions

• In the first one, the homologous cells separate,
  and in the second the sister chromatids separate

• Creating up to 4 cells with half the number of
  chromosomes as the parent cell.

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How does Meiosis create unique cells?

• During Prophase 1 crossing over happens to the
  homologous pairs to create new combinations of DNA

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Homologous pair One from mom, one from dad
Crossing Over
Unique cells due to crossing over
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