Mitotic Cell Division
Learn preparing and staining procedure to identify
the stages of mitosis in onion root tip.
To differentiate between the different stages of
Calculate the mitotic index.
Types of Cell Division
Producestwo new daughter cells with the same
number and kind of chromosomes as the parent cell
Reduction division produces progeny cells with one-
half the genetic content and number of chromosomes
as parent cell
– Mitosis occurs in order for organisms to grow and
– In order to replenish dead or dying cells such as
skin cells, and cells in the digestive tract.
– process of nuclear division (division of genetic
– Process of dividing cytoplasm/cell
The Cell Cycle
The life of a cell is divided into three stages known as
the cell cycle:
cell carries out normal functions and prepares to
nucleus divides splits into two
cell and contents divide into two daughter cells.
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:
replication of other cellular
There are 4 main phases:
Cytokinesis (division of the
cytoplasm) follows and one cell
Major processes during this phase:
Chromosomes condense and form
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
The nucleolus and the nuclear
membrane disappear. The mitotic
apparatus the spindle, begins to
organize within the cell
aligned at midpoint or
equator between poles of
are at their thickest and
They are easily identified as
two longitudinally double
replicates and splits
The sister chromatids
separate and are pulled
to opposite sides of the
Chromosomes now uncoil
Nuclear envelope reappears and
surrounds the chromosomes
The cytoplasm and all its contents are
divided between the 2 daughter cells
membrane creates between the 2 new
In plants, such as the onion root tip
cells, this is seen as the formation of a
Stages of mitosis in onion root tip cells
Mitosis in Root Tip
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
Slides & cover slips
Fresh onion root tips
Fixative ( methanol-acetic acid 3:1 v/v)
1 M HCl
Paper towel, or absorbent paper
Cut 2-3 mm of onion root
Use forceps to transfer an onion root tip into the cup of
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
Cover the root tip with one to two drops of 45% acetic
Put a cover slip over the root, put a paper towel or
other absorbent paper and with your thumb firmly press
21 on the cover slip.
Observe your preparation under the low power (X10) of a
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
Record your data in the table
Calculate the percentage of cells in each phase and record in
A measure for the proliferation status of a cell
It is defined as the ratio between the number
of cells in mitosis and the total number of