Download Unit 11: Review Cell Division

I. Mitosis in animal cells
Unit 11: Review
Cell Division
In animals, fertilization results in the production of a diploid cell called a zygote. The
zygote divides resulting in a ball of cells called a blastula. An image of a slide of a
whitefish blastula was observed.
One cell of the
blastula
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Mitosis in animal cells continued
blastula cross section
Mitosis in animal cells continued
Microscopic view, 400X
Interphase
Microscopic view, 400X
Most of the cell’s time (90-95%) is spent at
interphase. This is not a stage of mitosis but
rather precedes it.
Prophase
This is the first stage of mitosis.
Appearance of cells in interphase
Appearance of cells in prophase
The animal cells in general appear round.
The cell in interphase will have an intact
nuclear membrane. You can see a
nucleolus in this cell.
The cell in prophase will have beading DNA
because chromatin is condensing into
chromosomes. There is no arrangement of
chromosomes.
chromosomes
nucleus
chromatin
nucleolus
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Cell in prophase
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Cell in interphase
Mitosis in animal cells continued
Mitosis in animal cells continued
Microscopic view, 400X
Metaphase
Microscopic view, 400X
Anaphase
The prefix ‘meta-’ means middle. In metaphase
the centromeres of chromosomes line up at the
equatorial plate.
The centromeres replicate and sister
chromatids pull apart.
Appearance of cells in metaphase
Appearance of cells in anaphase
The cell in metaphase will have the centers of
chromosomes at the equator of the cell. The
loose arms will fall to either side of the equator.
The cell in anaphase will have separating sister
chromatids.
Centromeres line up
at the equator of cell
Sister chromatids
are pulling apart
Cell in anaphase
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Cell in metaphase
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Mitosis in animal cells continued
Mitosis in animal cells continued
Microscopic view, 400X
Telophase
Microscopic view, 400X
Cytokinesis
This stage marks the end of mitosis.
Cytokinesis is not a part of mitosis. It is the
division of the cytoplasm and its content
(except for the DNA). It is an event that
overlaps with the last part of mitosis. It
can be seen as early as anaphase.
Appearance of cells in telophase
The cell in telophase will have 2 collections
of chromosomes because the sister
chromatids are being pulled in opposite
directions. The separated sister chromatids
are then called daughter chromosomes.
Appearance of cytokinesis
A cleavage furrow (pinching inward)
forms to separate the cytoplasm of a
cell. This cell shows cytokinesis
overlapping with telophase.
Two collections of
chromosomes
Cell in telophase
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Cleavage furrow
forms in cytokinesis
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Mitosis in animal cells continued
The following slides contain
pictures of plastic cell
models.
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Mitosis in animal cells continued
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Prophase
Interphase (before mitosis)
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Mitosis in animal cells continued
•
Cytokinesis
Prophase (late – also called
prometaphase)
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Mitosis in animal cells continued
•
Metaphase
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Mitosis in animal cells continued
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Anaphase
Mitosis in animal cells continued
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Telophase
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II. Mitosis in plant cells
Mitosis in plant cells continued
Microscopic view, 400X
In plants a region called the meristem is actively growing
and results in elongation of tips (stems and roots) and
expansion of girth. An image of a slide of Allium
(onion) root tip will be observed.
Interphase
Most of the cell’s time (90-95%) is spent at
interphase. This is not a stage of mitosis but
rather precedes it.
The cell cycle includes Interphase (G1, S G2) and M phase
(mitosis and cytokinesis). We examined cells in
interphase, mitosis (prophase, metaphase, anaphase,
and telophase), and undergoing cytokinesis.
Appearance of cells in interphase
Onion root tip
cross section
Plant cells in general appear as squares.
The cell in interphase will have an intact
nuclear membrane. You can see a
nucleolus in this cell.
nucleolus
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Continue
Cell in interphase
Mitosis in plant cells continued
Mitosis in plant cells continued
Microscopic view, 400X
Prophase
Microscopic view, 400X
Metaphase
This is the first stage of mitosis.
The prefix ‘meta-’ means middle. In
metaphase the centromeres of
chromosomes line up at the equatorial
plate.
Appearance of cells in prophase
Appearance of cells in metaphase
The cell in prophase will have beading
DNA because chromatin is condensing
into chromosomes. There is no
arrangement of chromosomes.
The cell in metaphase will have the
centers of chromosomes at the equator
of the cell. The loose arms will fall to either
side of the equator.
chromosomes
Equator of cell
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Cell in metaphase
Cell in prophase
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Mitosis in plant cells continued
Mitosis in plant cells continued
Microscopic view, 400X
Microscopic view, 400X
Anaphase
Telophase
The centromeres replicate and sister
chromatids pull apart.
This stage marks the end of mitosis.
Appearance of cells in telophase
Appearance of cells in anaphase
The cell in telophase will have 2
collections of chromosomes because
the daughter chromosomes are now at
opposite ends.
The cell in anaphase will have separating
sister chromatids. Daughter chromosomes
are separated sister chromatids.
Two collections
of daughter
chromosomes
Daughter
chromosomes
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Continue
Cell in telophase
Cell in anaphase
Mitosis in plant cells continued
Microscopic view, 400X
III. Pop Beads Exercise on Mitosis
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Cytokinesis
Cytokinesis is not a part of mitosis. It is
the division of the cytoplasm and its
content (except for the DNA). It is an
event that overlaps with the last part
of mitosis. It can be seen as early as
anaphase.
•
Our cell will have only one pair of chromosomes (2n = 2), a yellow and a red
chromosome. We will label the red chromosome as a maternal chromosome and the
yellow as a paternal chromosome. The yellow chromosome and red chromosome are
homologous chromosomes. Homologous chromosomes are similar in size, gene loci
(location of genes), and staining patterns. Homologous chromosomes are NOT
identical because even though they both have a same gene locus for eye color (both
have a gene for eye color) one may have a gene for blue eyes and the other may
have a gene for brown eyes.
NOTE: Our initial cell (parental cell) shows DNA in the form for chromosomes but we
know that DNA should be in the form of chromatin. We use chromosomes because it
makes it easier to display the DNA.
Appearance of cytokinesis
A cell plate forms to separate the
cytoplasm of a cell.
Cell plate
Initial cell
2n=2
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Cytokinesis
Note: please disregard the black pointer.
Homologous chromosomes v.
sister chromatids
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•
Homologous chromosomes: a pair of chromosomes
– One chromosome is from each parent
• One maternal chromosome (red)
• One paternal chromosome (yellow)
Chromosome
Two arms of a
chromosome
can be of
different sizes
Centromere
Replicated homologous chromosomes
– Two replicated chromosomes
• One replicated maternal chromosome (red)
– With 2 sister chromatids (identical chromosomes)
• One replicated paternal chromosome (yellow)
– With 2 sister chromatids
This replicated chromosome has
ONE centromere that will divide in
metaphase (and 2 sister
chromatids).
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Interphase: before Mitosis
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Interphase is the non-dividing stage of the cell cycle in which the cell is preparing to
divide. Interphase includes G1(first gap phase), S (synthesis) and G2 (second gap
phase). During the S phase, the cell replicates the DNA. At the end of interphase the
cell has twice the amount of DNA( but NOT twice the number of chromosomes)
than the initial cell. The cell is still 2n = 2.
Mitosis: prophase
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Prophase marks the beginning of mitosis. The DNA is condensed into chromosomes
and we could see it with a light microscope. The DNA is not arranged in any way.
The cell in prophase is also assembling the spindle apparatus (which we will not
show in our diagrams). You can see the spindle apparatus in your textbook
diagrams.
In the cell you have:
-2 chromosomes
(replicated chromosomes),
one red and one yellow
-2 centromeres, one red
and one yellow
Initial cell, 2n=2
End of interphase, 2n=2
2 chromosomes
(parental chromosomes)
Prophase
2 chromosomes
(replicated chromosomes)
2 centromeres
2 centromeres
Mitosis: metaphase
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In metaphase the centromere of each chromosome lines up at the equator.
Mitosis: anaphase
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In anaphase the cell elongates and the sister chromatids separate to opposite
poles.
equator
In the cell you have:
In the cell you have:
-2 chromosomes
(replicated chromosomes),
one red and one yellow
-4 chromosomes
(daughter chromosomes),
two red and two yellow
-2 centromeres, one red
and one yellow
-4 centromeres, two red
and two yellow
Metaphase
Anaphase
Mitosis: telophase
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Daughter cells
In telophase the cell also experiences a new event, cytokinesis. *Cytokinesis is NOT
part of mitosis but overlaps with it. In telophase the division of the chromosomes is
complete. The nuclear membrane will begin to reestablish in each resulting cell. The
daughter chromosomes revert back to chromatin. Telophase is the last stage of
mitosis.
•
Daughter cells are genetically identical to each other.
At each pole you have:
-2 chromosomes
(daughter chromosomes),
one red and one yellow
-2 centromeres, one red
and one yellow
Telophase
Daughter cells
2 poles
2n=2
*Cytokinesis differs for plant and animal cells. See textbook for details.
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IV. Meiosis
Meiosis continued
Meiosis is a form of cell division that occurs in the gonads (ovaries and testes) of
animals. The cells that result from this division are called gametes (ova and
sperm) and the process is called gametogenesis (the making of gametes).
Meiosis consists of two divisions, namely Meiosis I and Meiosis II.
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Interphase
Interphase precedes meiosis and is not a part of it. During interphase the
chromosome replicate.
Meiosis I
This stage consists of four sub stages; prophase I, metaphase I, anaphase I, and
telophase I
Cytokinesis
Cytokinesis is not a part of meiosis. During cytokinesis the cytoplasm of sperm cells
will be divided roughly in half but the cytoplasm of ova will be divided unequally,
retaining most of the cytosol in one of the two daughter cells.
Meiosis II
This stage consists of four sub stages; prophase II, metaphase II, anaphase II, and
telophase II.
Cytokinesis
Cytokinesis, again, is not a part of meiosis. The cytoplasm is divided a second
time.
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Meiosis continued
Spermatogenesis (making of sperm)
Meiosis continued
Oogenesis (making of the ovum)
Initial cells are found in the gonads (testes
in males and ovaries in females). The cell is
being prepared for meiosis.
Initial cell
Cells enter interphase (G1, S, G2) where the
DNA is replicated. This example will use 6
as its diploid number. DNA is in the form of
chromatin (although for the purpose of
seeing the DNA, it appears as
chromosomes in our example).
Before cells enter interphase, the DNA is not replicated. After interphase the DNA is
replicated. DNA appears in the form of chromatin at this stage (although for the
purpose of seeing the DNA, it appears as chromosomes in our example).
Initial cell
Prophase I is the first stage of meiosis.
Synapsis and crossing-over will occur. Four
sister chromatids will form a tetrad.
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Not replicated
Replicated
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Pictures are from plastic model boards
Meiosis continued
Spermatogenesis (making of sperm)
Oogenesis (making of the ovum)
Meiosis continued
Spermatogenesis (making of sperm)
Oogenesis (making of the ovum)
Telophase I. First DNA separation is
complete. The cell divides into
two.
Metaphase I. Tetrads line up in the
cell.
Prophase II. Each daughter cell
has a haploid number of
chromosomes.
Metaphase II. Replicated
chromosomes line up individually.
Anaphase I. Homologous
chromosomes pull apart from one
another. Cytokinesis overlaps with
anaphase I. Notice equal cytokinesis
in spermatogenesis but unequal
cytokinesis in oogenesis.
Continue
Continue
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Meiosis continued
Spermatogenesis (making of sperm)
Oogenesis (making of the ovum)
Meiosis continued
Spermatogenesis (making of sperm)
Oogenesis (making of the ovum)
Telophase II. The second DNA
separation is complete. You form four
haploid daughter cells.
Anaphase II. Chromosomes pull
apart and separate the sister
chromatids.
Spermatogenesis. You form four similar
daughter cells that will become sperm cells.
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Oogenesis. You form one ovum
and three polar bodies. The
three polar bodies cannot be
fertilized.
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Meiosis continued
Meiosis overview
Initial cell is diploid
(6 chromosomes or 3
pairs of chromosomes)
2 daughter cells are haploid
(each cell has 3 replicated
chromosomes
4 daughter cells are haploid
(each cell has 3 chromosomes)
End of Lab
Review ☺
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