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Mitosis and Meiosis
The creation of new cells.
Mitosis
 Cells divide to create new cells that are genetically
identical to the old cell. This process is called mitosis.
 Necessary for growth and development
 Necessary for tissue replacement
 Organ or tissue enlargement
 Production of reproductive cells
 Single-celled organisms divide to reproduce.
A Cross-Section of cell activity
Cell Cycle
Cell Cycle
 http://highered.mcgraw-
hill.com/sites/0072495855/student_view0/chapter2/a
nimation__control_of_the_cell_cycle.html
Five phases
 http://www.johnkyrk.com/mitosis.html
CELL CYCLE
INTERPHASE
Resting stage
Minor
changes
occur in
preparation
for division
The longest
phase
PROPHASE
-Chromatin threads
shorten, thicken and
become visible as
chromosomes
- Chromatids held
together at a single point
called the centromere
-Spindle formed from
protein fibers
-Chromosomes begin to
arrange in a linear
fashion.
- Nuclear membrane
disappears
METAPHASE
-Chromatid
pairs line up
along the
equator
- spindle fibers
attach to the
centromere
ANAPHASE
-Chromatids
separate
-Move to opposite
poles
-Chromatids
referred to as
chromosomes after
separating
- Same number of
chromosomes at
each pole
TELOPHASE
-Spindle breaks down
- nuclear membrane forms around
each set of chromosomes
- CYTOKINESIS
-Cytoplasm divides to form
two cells
-Animals cells—cell
membrane pinches inward
and forms a groove, which
deepens until the two cells
are separated
-Plant cells—cell plate
forms between the two
daughter cells
-Two new, identical cells
How it Works
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hill.com/sites/0072495855/student_view0/chapter2/a
nimation__how_the_cell_cycle_works.html
Chromosomes
 Shrimp
 Goldfish
 Sweet Potato
 Duck
 Dog
 Horse
 Guinea Pig
 Chinchilla
 Donkey
 Goat
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90
80
78
64
64
64
62
60
 Sheep
 Potato
 Human
 Rabbit
 Hamster
 Peanut
 Swine
 Cat
 Bean
 Cucumber
54
48
46
44
42
40
38
38
22
14
Tissue culture
 One offshoot of the study of mitosis is tissue culture.
 In tissue culture, the cells to be studied are removed
from the organism’s body and grown on a sterile,
artificial medium.
 When grown in this manner, typically normal cells
grow one layer thick on the surface of the sterile
medium and will undergo only 20 to 50 mitotic
divisions then cease to be able to reproduce.
Tissue culture
 the growth of tissues or cells separate from the
organism. This is typically facilitated via use of a
liquid, semi-solid, or solid growth medium, such as
broth or agar.
 Typically, when all cells are touching neighbors all
around, they stop dividing. This phenomenon is
known as contact inhibition.
 In sharp contrast, cancer cells will not stop growing
with one layer on the surface of the medium, but grow
multiple layers and fill the dish. They do not exhibit
contact inhibition: they don’t stop growing when
touching on all sides. Also cancer cells appear to have
no limit to the number of generations they can
produce.
 Tissue culture is now a widely-used means of more
effectively and quickly finding the right drugs to treat
cancer.
 Typically, in the past, people with cancer were
subjected to one toxic drug after another in hopes of
finding one that would be effective against that
particular cancer.
 Now, when a person is diagnosed with cancer, a biopsy
can be taken and a number of cultures of cells can be
grown.
 Each of these cultures can be subjected to a different
drug, thus enabling doctors to find the right drug
sooner, while it may still be of help, and without
needlessly subjecting the person to many kinds of
toxic chemicals
Different Rates
 Within our bodies, different cells do mitosis at
different rates.
 Skin cells continuously do mitosis and divide, thus our
skin is constantly renewed and repaired.
 In sharp contrast, most nerve cells stop doing mitosis
soon after birth or slow down considerably.
 Liver cells are somewhere in between. In a healthy
adult, liver cells normally do not divide, but can divide
to repair minor damage.
Gamete division
Process of forming germ cells
 Occurs in reproductive organs only
 Gametes are formed by a maturation division –
separates the pairs of chromosomes
 Has two nuclear divisions
 Gametes have only 1 member from each chromosome
pair
 Sex determination
Form gametes
 n = chromosomes in each gamete
 Diploid number = 2n
 Haploid number = 1n or n
 Female carry (n-1) autosomes and 1 x chromosome
 Male carry (n-1) autosomes and 1 x or y chromosome
 y is smaller than the x and carries very little genetic
information
Chromosome numbers
 Mammals
 Male = xy
 Female = xx
 Birds, butterflies and moths
 Male = xx zz
 Female = xy zw
 Reptiles – gender is determined by the temperature
that the egg is incubated at.
 Germ cell multiplication
 Egg and sperm cells multiply. The cell contains the total number of
chromosome pair. This division is mitosis.
 Growth period
 During the maturation process, the cell prepares for the
chromosome pair to split.
 Chromosome pairing
 Chromosome pairs align themselves
 Chromosome reduction
 The cells (gametes) divide and the chromosome pairs separate.
 Each new gamete contains one half the total number of
chromosomes.
 Gamete division
 The new gametes continue to divide through mitosis
Meiosis
 http://www.johnkyrk.com/meiosis.html
Interphase I
- Chromatin
threads shorten
and thicken
- DNA replicates
itself
Prophase I
-Chromatin threads shorten
and thicken
-Chromosomes become visible
-Each chromosome
made of 2 identical
chromatids joined at
the centromere
-Homologous
chromosomes begin to
move toward each
other
-Tetrad—the
arrangement formed
when homologous
chromosomes move
close to each other = 4
chromatids
-Tetrads move toward the
middle of the cell
Metaphase I
Tetrads line up
along the cell’s
equator
-
Anaphase I
Homologous
chromosomes of the
tetrad separate and
move to opposite
poles
-Chromatids of
individual
chromosomes don’t
separate yet
-
Telophase I
-Cytoplasm divides
-First stage of meiosis is
complete
-Two haploid daughter cells
have been produced
Each daughter
cell contains only one
chromosome of each pair
that was in the parent cell
Total number of
chromosomes in each
daughter cell equals half
the number of
chromosomes in the
original parent cell
Prophase II
Chromatids become
shorter and thicker
-Spindle begins to
form
-
Metaphase II
Chromosomes
line up along the
cell equat0r
-Spindle begins
to form
-
Anaphase II
Chromatids of
each
chromosome
separate and
migrate to
opposite poles
-
Telophase II
-Nuclear membrane
forms around each set of
chromatids
-Chromatids now called
chromosomes since they
are no longer joined
-Cytoplasm divides
-Four haploid cells form
with a different
chromosome make-up
than the parent cell
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hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/si
tes/dl/free/0072437316/120074/bio19.swf::Stages%20of
%20Meiosis
 chi·as·ma

/kaɪˈæzmə/ Show Spelled[kahy-az-muh] Show IPA
 –noun, plural -mas, -ma·ta /-mətə/
show+spelled">Show Spelled[-muh-tuh] Show IPA. 1.
Anatomy . a crossing or decussation, as that of
the optic nerves at the base of the brain.
 2. Cell Biology . a point of overlap of paired chromatids
at which fusion and exchange of genetic material take
place during prophase of meiosis.
Meiosis/mitosis comparison
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hill.com/sites/0072495855/student_view0/chapter2/a
nimation__comparison_of_meiosis_and_mitosis__qui
z_1_.html
 http://www.pbs.org/wgbh/nova/miracle/divi_flash.ht
ml