The Process of Cell Division
The Cell Cycle
The cell cycle consists of three stages:
– Interphase – stage before the cell divides
– Mitosis - the nucleus divides
– Cytokinesis - the whole cell divides
Stage One - Interphase
Most of the life
of a cell is spent
in a period of
growth and
development
called
interphase.
Chromosomes
Chromosomes are
structures in the
nucleus that contain
DNA. During
interphase, you can’t
see chromosomes but
they are actively
replicating themselves.
Each chromosome is
held together in the
middle by a centromere.
Once the chromosomes
have doubled, the cell is
ready to begin dividing.
centromere
Stage Two - Mitosis
• The cell that is dividing is called
the parent cell.
• Mitosis is the process in which a
cell nucleus divides into two new
nuclei. Each new nucleus has the
same number of chromosomes as
the parent cell.
The Four Steps of Mitosis
Mitosis is described as a series
of four steps.
1.
2.
3.
4.
Prophase
Metaphase
Anaphase
Telophase
Step 1 - Prophase
During prophase, the chromosomes
become visible. The membrane
around the nucleus disappears.
Spindle fibers begin to stretch
across the cell.
whitefish mitosis
Step 2 - Metaphase
In metaphase, the chromosomes line
up in the middle of the cell. Each
centromere attaches itself to a spindle
fiber.
Step 3 - Anaphase
In anaphase the centromere divides
and the two pieces (strands) of the
chromosome separate. The separate
strands begin to move away from each
other toward the opposite sides of the
cell.
Step 4 - Telophase
In telophase, spindle fibers disappear.
The chromosomes become harder to
see. A nuclear membrane forms
around each set of chromosomes.
whitefish mitosis
Stage Three – Cytokinesis
Animal Cells
In animal cells the cytoplasm
pinches in to form the new cells.
The new cells then begin a period of
growth and are in interphase.
Cytokinesis - Plant Cells
Plant cells have rigid
cell walls so they can’t
pinch apart like animal
cells do. Instead, a cell
plate forms between
the two new nuclei.
New cell walls form
along the cell plate.
New cell walls
Onion root tip mitosis
46 Chromosomes
Most of the cells in
your body have 46
chromosomes. Each
new cell produced by
mitosis will also have
46 chromosomes.
Humans have 46
chromosomes
Human Chromosomes
Chromosome Numbers
Fruit fly cells have eight
chromosomes. New fruit
fly cells produced by
mitosis will each have
eight chromosomes.
Carrot cells have eighteen
chromosomes before and
after mitosis.
Mitosis in Onion Cells
interphase
prophase
metaphase
anaphase
telophase
Can You Find Cells in the
Different Phases of Mitosis?
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