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Cell Division
Your body is composed of more
than a billion cells
Why must cells divide?
They are continually
dying and must
produce new cells
An identical copy of
your hereditary
information is in
the nucleus of
each and every
body cell called a
somatic cell
dbb.urmc.rochester.edu/.../photo_gallery.
Chromosomes

The genetic information or blueprint that
is organized into 46 chromosomes (each
contains about one to two thousand
genes)
Karyotype
Human
chromosome
number: 46
Karyotype – order of
chromosomes
from tallest to
smallest.

Every time a cell divides it must copy the
chromosomes
Goal of Mitosis


Baby
is to allow for growth
maintain tissues
Grow to adult

Another way to look at this is like this:
Stages of Mitosis is IPMAT
Mitosis animation: http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.html
Interphase



Time between divisions – cell spends 90%
of its life here
DNA is copied here
Typical human cell divides every 24 hours
Inside – looks like..
Diploid - 3
chromosome pairs,
6 individual
chromosomes



Your nucleus initially contained six unreplicated chromosomes, and now it
contains six replicated chromosomes.
The two identical copies of each
chromosome are called sister chromatids
They remain attached at a point
called the centromere
Prophase



Chromosomes
condense (are
visible)
Sister chromatids
pair up.
Nuclear membrane
disappears
Pro-metaphase-Start moving to
sides
Metaphase

Paired chromatids line
up in the middle of
cell
Anaphase

Chromatids are pulled into the
apart. They are dragged through
the cytoplasm (V-shaped)
Telophase



Daughter
chromosomes reach
the poles
Cells start to separate
Nuclear membrane
re-forms
Cytokinesis

The two daughter
cells separate
(Cell Cutting)

At the end of Mitosis,
each daughter cell has
an identical set of
duplicate chromosomes
They are called Somates –
body cells
Mitosis Stages
Mitosis animation
http://www.sumanasinc
.com/webcontent/anim
ations/content/mitosis.h
tml
Interphase is subdivided
G1 – Gap 1 or growth 1

cell carries out normal functions
G1 is a period of activity in which cells do most of their
growing, increasing in size and synthesizing new
proteins and organelles
S
Synthesis
– DNA is copied to prepare to divide
 it synthesizes (to make) a duplicate set of
DNA
G2
G2 – Gap 2

is where the organelles and molecules required for
cell division are produced.
M phase then Cytokinesis
Mitosis takes about an hour (most time
spent during G1, S and G2 phase)
PMAT

Check points




G1 – Checks DNA damage before begins
replication (S phase), if damaged then
repaired or self destructs if cannot repair.
G2 – Checks DNA to see if properly copied
during S phase
M – checks to ensure spindle fibers attach
properly during metaphase
http://www.cellsalive.com/cell_cycle.htm
How does Mitosis lead to Caner?
Cancer is basically a disease of mitosis
What is happening?
The normal checkpoints that regulate
mitosis are ignored or overridden by
cancer cell.
How does it occur?
a change in function or a DNA mutation
occurs in one of several genes (proteins)
that normally function to control growth
Result
Once these crucial Cell Cycle genes start
behaving abnormally, cancer cells start to
proliferate wildly by repeated, uncontrolled
mitosis
Tumor production:
http://www.youtube.com/watch?v=_ZEysI
hDsok&feature=related
Examples:
(1)
p53 protein can
senses DNA
damage and halts
progression of cell
cycle. Also
known as tumor
suppressor gene.
However, p53 is
mutated in over
50% of all human
cancers.
(1)
BRCA 1 gene, the
"Breast Cancer
Gene" normally
repairs mutations in
PTEN gene which
suppress tumor
formation
but if a gene contains
mutations such that
BRCA1 does not
work properly, tumor
formation can begin
Meiosis


Cell Division to make
sex cells
(sperm and eggs)
Chromosome number is
halved creating these
cells

ex. 46  23
Meiosis animation:
http://www.sumanasinc.c
om/webcontent/animatio
ns/content/meiosis.html
Diploid vs. Haploid
Diploid – two or a pair of
chromosome
Haploid – 1 set of chromosomes
Examples:
Diploid = 2
4
8
Haploid = 1
2
4
YOU TRY: If the diploid
chromosome number is 28,
what is the haploid number?
Stages :
IPMAT
then
PMAT II
Crossing Over
(independent
Assortment) tetrad
Crossing Over


Homologous
chromosomes can
swap information,
increasing variability
in offspring
Takes place in
prophase
Tetrad – set of 4
chromosomes
Homologous Chromosomes


The two versions of each chromosome
One from mom, one from dad
Gametes
Gametes are sex cells
Sperm
Egg
Each are haploid – half the number of
original set of chromosomes
Diploid = 46
Haploid = 23
Spermatogenesis

Creates four functional sperm cells
Oogenesis

Creates one functional Ovum (egg) and 3
polar bodies
Gametes – sex cells
Products of meiosis in
males formed in
testes?
A: 4 sperm
Products of meiosis in
females formed in
ovaries?
A: 1 functional egg (the
other 3 cells are not
functional and are
reabsorbed by the body?
Humans have 46
homologous chromosomes
(23 pairs)
Stages of Meiosis
Interphase: same as Mitosis
Prophase 1: Same except for
Crossing - over can occur – leads to independent assortment (life
is a box of chocolates)
Metaphase 1: Same except that form a tetrad
Homologous chromosomes that align at the equatorial plate.
Anaphase 1: Same except that the Homologous pairs separate
with sister chromatids remaining together.
Telophase 1: Same except each daughter contains only one
chromosome of the homologous pair (not a pair of
chromosomse).
Second Stage
Prophase 2: same as mitosis
Metaphase 2: same as mitosis
Anaphase 2: Centromeres divide and sister chromatids
migrate separately to each pole. (same as mitosis)
Telophase 2: Four haploid daughter cells instead of two.
. Daughter cells have half the number of
chromosomes found in the original parent cell and
with crossing over, are genetically different.
Timing in Meiosis
When do Females produce their eggs?
 Prior to birth
What do Males produce sperm?
 Once hit puberty

Helpful saying
I don’t use “Mi-Toes-es” for making sperm or
eggs!
Differences between Mitosis and
Meiosis
Mitosis
IPMAT
Diploid
Somate
2 cells
Meiosis
IPMAT I & PMAT II
Haploid
Gamete
4 cells

Non-Disjunction- when chromosomes do not
separate correctly during meiosis.
End up with 47 or 45 in each new cell.
Example:
Downs Syndrome = Trisomy 21 (3 chromosomes 21)
Turner’s Syndrome = one X and no second sex
chromosome
Trisomy 21