Cell Division
You started as one
cell,
but now you are
trillions and trillions of
cells all genetically
identical to that first
one.
Let’s Review…
Cell Cycle and Mitosis
What are the 3
stages of the cell
cycle?
Partner A: The 3 stages of the cell
cycle are____________.
Partner B: I agree/disagree because
_________________.
Interphase
98% to 99.999% of the cells
life cycle
This is when the cells do the
job they are meant to do.
But there are things that
the cell does to get ready
for the next Mitosis.
Interphase -broken into 3 different parts:
1. G1 - First Growth
The cell grows in size
and increases # of
organelles
2. S - Synthesis
DNA replicates during
this time
Happens rapidly
3. G2 - Second Growth
Increase the size of
the cell again and
increase the # of
organelles again
What are the 4
stages of mitosis?
Partner B: The 4 stages of mitosis
are__________.
Partner A: I agree/disagree because
_______________.
Mitosis
4 stages:
1. Prophase:
The Centrioles begin to move apart.
Chromosomes thicken
The Nuclear membrane disappears
2. Metaphase:
The centrioles are at the “poles” of the cell
The chromosomes line up in the middle
of the nucleus
3. Anaphase:
The Chromosomes are pulled toward the
centrioles by spindle fibers
4. Telophase:
The nucleus begins to reform and the
cell begins cytokinesis
Cells divide in two different stages:
First – Mitosis ( my-`toe-sis)
Second – Cytokinesis
(Sye-toe-kin-E-sis)
- Dividing the Nucleus.
- Dividing the rest of
the cell.
How do you divide the nucleus?
You tear it in two!!
How many Chromosomes are in
each of your cells?
46 individual ones - (23 pairs)
Diploid Cells
(2n)
A cell containing a full
set of chromosomes;
somatic or body cells
Haploid Cells
(n)
A cell containing
half a set of
chromosomes;
gametes or sex cells
Homologous Chromosomes –
Chromosomes that have the
same length and gene locations;
one from mom and one from dad.
The process
by which
two haploid
gametes
combine to
form a new
diploid cell
is called
fertilization.
Meiosis:
The process of dividing a
diploid cell to create haploid
sex cells called Gametes
Gamete - sperm or egg
Goes through TWO cell
divisions.
Starts with 1 parent cell
and ends up with 4
genetically different
daughter cells.
Meiosis 1
Interphase 1
Cell goes from 46 to
92 Chromosomes
Cross over occurs
Prophase 1
Parts of “sister”
chromosomes may exchange
sections; this allows for
genetic variation
Metaphase 1
Chromosomes line up
Anaphase 1
Chromosomes pull apart
Telophase 1
2 cells with 46 individual chromosomes but
not identical
Meiosis 2
NO ITERPHASE!!
Prophase 2
Begins again with the two 46
chromosomes cells
Metaphase 2
Same as Meiosis 1
Anaphase 2
Same as Meiosis 1
Telophase 2 &
Cytokinesis
Creation of 4 completely individual
cells with 23 chrosomes each
Genetic Variation
How the chromosomes line up in metaphase I of
meiosis is a random process that means every
gamete created will be genetically different from
the parent cell and from each other.
Crossing over in prophase
I of meiosis also allows for
greater genetic variation
within a species.
Why is genetic
variation
important?
Partner A: I think genetic variation
is important because___________.
Partner B: Genetic variation is also
important because _____________.
Please take the last few
minutes of class to look
over your homework. Finish
answering any questions
you skipped and fix any you
answered incorrectly.
When you are finished, turn
it in to Mrs. Fletcher.