Mitotic Cell Division
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Objectives
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Learn preparing and staining procedure to identify
the stages of mitosis in onion root tip.
To differentiate between the different stages of
mitosis.
Calculate the mitotic index.
Types of Cell Division
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Mitosis
 Produces
two new daughter cells with the same
number and kind of chromosomes as the parent cell
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Meiosis
 Reduction
division produces progeny cells with onehalf the genetic content and number of chromosomes
as parent cell
 Produces gametes/spores
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Mitosis
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Purpose:
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Karyokinesis
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process of nuclear division (division of genetic
material)
Cytokinesis
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Mitosis occurs in order for organisms to grow and
develop.
In order to replenish dead or dying cells such as
skin cells, and cells in the digestive tract.
Process of dividing cytoplasm/cell
The Cell Cycle
The life of a cell is divided into three stages known as
the cell cycle:
1. Interphase:
cell carries out normal functions and prepares to
divide
2. Mitosis:
nucleus divides splits into two
3. Cytokinesis:
cell and contents divide into two daughter cells.
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Cell Cycle
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G0
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Interphase
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This phase consist of the G1,S,
and G2 phases of the cell cycle.
The chromatin is diffuse.
It may not look like much is going
on here, but there is a lot of
activity because the cell must
prepare for Mitosis:
protein synthesis,
DNA synthesis,
replication of other cellular
structures.
Mitosis
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There are 4 main phases:
 Prophase,
 Metaphase,
 Anaphase,
 Telophase.
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Cytokinesis (division of the
cytoplasm) follows and one cell
becomes two.
Mitosis: Prophase
Major processes during this phase:
 Chromosomes condense and form
visible bodies
 Chromosomes become thicker,
shorter, and easily visible when
stained under the light microscope.
 Two “sister chromatids” join near
their middle at a structure called the
centromere.
 The nucleolus and the nuclear
membrane disappear. The mitotic
apparatus the spindle, begins to
organize within the cell
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Mitosis: Metaphase
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Chromosomes
become
aligned at midpoint or
equator between poles of
the cell
are at their thickest and
shortest structure.
They are easily identified as
two longitudinally double
sister chromatids.
Mitosis: Anaphase
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The centromere
replicates and splits
The sister chromatids
separate and are pulled
to opposite sides of the
cell
Mitosis: Telophase
Chromosomes now uncoil
 Nuclear envelope reappears and
surrounds the chromosomes
Cytokinesis
 The cytoplasm and all its contents are
divided between the 2 daughter cells
(cytoplasmic division)
 membrane creates between the 2 new
daughter cells
 In plants, such as the onion root tip
cells, this is seen as the formation of a
cell plate
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Stages of mitosis in onion root tip cells
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Mitosis in Root Tip
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In a growing plant root, the cells at the tip of
the root are constantly dividing to allow the
root to grow.
Because each cell divides independently of
the others, a root tip contains cells at
different stages of the cell cycle.
This makes a root tip an excellent tissue to
study the stages of cell division
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Experiment
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Materials
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Slides & cover slips
Microscope
Fresh onion root tips
Fixative ( methanol-acetic acid 3:1 v/v)
Forceps
1 M HCl
Razor blade
Stain
Paper towel, or absorbent paper
Method
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Cut 2-3 mm of onion root
Use forceps to transfer an onion root tip into the cup of
HCl.
Leave for 4 minutes
Transfer the root tip to the cup containing fixative and
leave it for 4 minutes.
Then place the root tip on a slide.
Cover the root tip with a few drops of stain for 2
minutes
Cover the root tip with one to two drops of 45% acetic
acid
Put a cover slip over the root, put a paper towel or
other absorbent paper and with your thumb firmly press
on the cover slip.
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Observe your preparation under the low power (X10) of a
microscope
Search the slide to find cells in various stages of cell division,
once you have located cells in division, change to high power
(X40) & try to observe several stages of division.
Record the number of cells in each stage. Count at least
three full fields of view. You should have counted over 200
cells.
Record your data in the table
Calculate the percentage of cells in each phase and record in
the table
Mitotic index
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A measure for the proliferation status of a cell
population.
It is defined as the ratio between the number
of cells in mitosis and the total number of
cells.
Animation
http://www.youtube.com/watch?v=s1ylUTbX
yWU
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Interphase
Prophase
Metaphase
Anaphase
Telophase
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