Mitosis and Meiosis
Basic Cell Biology
Topic 3202C, 3025G,
3025H
Melinda Klockziem
Mitosis
How do cells reproduce?
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•
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Mitosis -- the cells divide to produce two
identical cells.
Genetic material in both is identical
End up with two diploid cells
Mitosis is necessary for growth and
maintenance.
Stages of mitosis

1. Interphase
– The cell doubles its
DNA
– Nucleoli and nuclear
membrane present
http://www.erin.utoronto.ca/~w3bio380/Lectsked/Supple2/
meiosis.html
http://www.bioweb.uncc.edu/biol1110/Stages.htm
Stages of mitosis

2. Prophase
– Sister Chromatids
shorten and thicken
– Chromosomes
visible
– Nuclear membrane
disappears
– Chromosomes have
“X” shape joined at
the centromere
http://www.erin.utoronto.ca/~w3bio380/Lectsked/Supple2/meiosis.html
http://www.bioweb.uncc.edu/biol1110/Stages.htm
Stages of mitosis

3. Metaphase
– Sister chromatids
line up along
equator of the cell
– Attach to spindle
fibers which act a
guide to separate
the sister chromatids
http://www.erin.utoronto.ca/~w3bio380/Lectsked/Supple2/meiosis.htm
l
http://www.bioweb.uncc.edu/biol1110/Stages.htm
Stages of mitosis

4. Anaphase
– Sister chromatids
separate
– Sister chromatids
move to opposite
ends of the cell
http://www.erin.utoronto.ca/~w3bio380/Lectsked/Supple2/meiosis.html
http://www.bioweb.uncc.edu/biol1110/Stages.htm
Stages of mitosis

5. Telophase
– Nuclear membranes
reform
– Two new cells are
separated
– Cytokinesis occurs
http://www.erin.utoronto.ca/~w3bio380/Lectsked/Supple2/meiosis.html
http://www.bioweb.uncc.edu/biol1110/Stages.htm
Animation of Mitosis
Cell Alive Website
Cancer and Mitosis
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Mitosis is necessary, but…
Uncontrolled mitosis is cancer.
Cancer cells divide without control.
Cancer cells create a mass in tissues or
organs.
Two types of Cancer
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–
Benign
Malignant
Mitosis Yarn Lab
Meiosis
Background Information

Chromosome Numbers
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Haploid or N
Humans 23 Haploid number (N)
Chromosomes are in pairs
Humans have a total of 46 chromosomes or 2N
(diploid)
Meiosis reduces 2N to N
Thus when sperm and ova meet and combine at
fertilization the resulting embryo will have 2N
How else do cells reproduce?

Meiosis is the reproduction of animal sex
cells
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
Ova and sperm
Happens in two stages
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–
Two divisions of the cell compared to only one
division in mitosis
End up with four haploid cells
Stages of Meiosis I

Prophase I
– Chromosomes
thicken and
becomes visible
– Chromosomes are
present in
homologous pairs
http://www.erin.utoronto.ca/~w3bio380/Lectsked/Supple2/
meiosis.html
Stages of Meiosis I

Metaphase I
– Homologous pairs
line up on the axis
of the dividing cell
opposite from each
other.
http://www.erin.utoronto.ca/~w3bio380/Lectsked/Supple2/
meiosis.html
Stages of Meiosis I

Anaphase I
– Homologous pairs of
chromosomes leave
each other and are
pulled towards
opposite poles by
spindle fibers
http://www.erin.utoronto.ca/~w3bio380/Lectsked/Supple2/meiosis.html
Stages of Meiosis I

Telophase I
– The cells physically divide
– Each daughter cell now contains one
chromosome from each pair
– Reduction Division
 Number
of chromosomes
is reduced from diploid to
haploid.
http://www.erin.utoronto.ca/~w3bio380/Lectsked/Supple2/
meiosis.html
Stages of Meiosis II

Prophase II
– Chromosomes still
duplicated
http://www.erin.utoronto.ca/~w3bio380/Lectsked/Supple2/
meiosis.html
Stages of Meiosis II

Metaphase II
– Sister chromatids
line up on the axis
of the cell.
http://www.erin.utoronto.ca/~w3bio380/Lectsked/Supple2/
meiosis.html
Stages of Meiosis II

Anaphase II
– The sister
chromatids are
pulled apart at the
centromere by
spindle fiber
http://www.erin.utoronto.ca/~w3bio380/Lectsked/Supple2/
meiosis.html
Stages of Meiosis II

Telophase II
– Nuclear membrane
reforms
– Each of the four
final haploid cells or
gametes contain one
strand from the
original homologous
pair of
chromosomes.
http://www.erin.utoronto.ca/~w3bio380/Lectsked/Supple2/meiosis.html