© Amy Brown Science
Cell division is the process
by which cellular material is
divided between two new
daughter cells.
1 Mother Cell  2 Daughter cells.
The two daughter cells will be….
…identical to each other and to
the mother cell.
copy its chromosomes
Each cell must first __________________
before cell division occurs.
Each daughter cell gets a complete
copy of that information.
Cell division occurs in two main stages:
Mitosis – The division of the nucleus
Cytokinesis – The division of the cytoplasm
Results of
Mitosis
Importance
of Mitosis
• In unicellular plants and animals,
it results in new offspring by
asexual reproduction.
• In multicellular organisms, it
results in the growth and repair
of the organism.
• The two new cells are
exact duplicates.
• Insures that the new cells
will be able to carry on the
same functions as the
mother cell.
There are many
proteins found on the
inside and the outside
of the cell that
regulate cell division.
Some of these
proteins are
responsible for
starting and stopping
cell division.
Cell Cycle
Regulators
Other proteins seem
to speed up or slow
down the cell division
process.
These proteins send out
signals that prevent
excessive cell growth.
This keeps the tissues of
the body from disrupting
one another.
Uncontrolled Cell Growth
Cancer cells do not respond to the
signals that regulate the growth of cells.
Cancer cells divide uncontrollably and
form masses of cells called tumors.
If the cells in a tissue
grow uncontrollably,
the consequences may
be severe.
All cancers have one thing in common:
The protein regulators that control the
cell cycle have failed to do their job.
These tumors can
damage the surrounding
healthy tissues.
Phases of Meiosis
Purpose is to
Occurs in
reduce the
the sex chromosome
cells only: number of
the egg and
the egg
and sperm. sperm by
half.
Meiosis, like
mitosis, is
preceded by the
replication of
chromosomes.
Unlike mitosis, this
replication is then
followed by two
divisions: meiosis I
and meiosis II.
The stages of meiosis I and II
Interphase
Prophase I
Prophase II
Telophase I
(and cytokinesis)
Metaphase I Anaphase I
Metaphase II
Anaphase II
Telophase II
(and cytokinesis)
chromatin
nuclear
membrane
cell membrane
nucleolus
Homologous chromosomes
sister chromatids
Tetrad
sister chromatids
nonsister chromatids
chiasmata: site
of crossing over
Tetrad
variation
Another Way Meiosis Makes Lots of
Different Sex Cells – Crossing-Over
Crossing-over multiplies the already huge number of
different gamete types produced by independent
spindle fiber
centrioles
aster
fibers
OR
metaphase plate
metaphase plate
metaphase plate
metaphase plate
n=2
sex cell
sperm
n=2
n=2
2n=4
haploid (n)
n=2
n=2
diploid (2n)
n=2
meiosis I
meiosis II
n=23
egg
sperm
n=23
2n=46
zygote
Meiosis produces four haploid
cells that are different.
In males, meiosis results in 4
sperm cells.
In females, 4 cells are produced,
but only one will become an egg
cell. All of the cytoplasm and all
of the organelles are put into one
egg cell. The other three cells will
never be functional.
Mitosis occurs in all cells of the
egg and sperm
_____
body except _____________.
Meiosis only occurs in the
egg and sperm
formation of _____________.
diploid cell
In meiosis, each _______
divides ______
twice to produce a total of
4 cells.
___
diploid cell divides
In mitosis each _______
2 cells.
once to form ___
_____
In meiosis, each of the four cells contains
half the number of chromosomes as the
_____
parent cell.
In mitosis, each new cell contains the
same number of chromosomes as the
______
original cell.
In mitosis, the homologous pairs do not
tetrads
come together to form _______.
In meiosis, the homologous pairs do come
tetrads While the
together to form _______.
crossing over
chromosomes are in tetrads, _____________
may occur. There will be no crossing over in
mitosis
_______.
In meiosis, the four haploid cells
different combinations of
contain ________
chromosomes from each other.
In mitosis, the new cells contain
identical copies.
________