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LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Mitosis & Meiosis
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
Phases of the Cell Cycle
• consists of two phases
– Mitotic (M) phase = mitosis and
cytokinesis)
– Interphase = cell growth and copying
of DNA in preparation for cell division
• Interphase - about 90% of the cell
cycle
– can be divided into sub-phases
– G1 phase -“first gap” – preparation for
S phase
– S phase “synthesis” – duplication of
DNA
– G2 phase - “second gap”- preparation
for mitosis
http://www.wisconline.com/objects/in
dex.asp?objID=AP136
04
Some terms to know
-genome = all the DNA within the
nucleus
-parent cell = cell about to undergo
division (either mitosis or meiosis)
-daughter cell = cell that results from
either mitosis or meiosis
-somatic cell = any cell within the body
other than an egg or sperm
-a somatic cell has two complete sets of
chromosomes
-one set is called the haploid
number of chromosomes (n)
-therefore the somatic cell is said to be
diploid (2n)
e.g. humans n = 23 (2n = 46)
-germ cell or gamete = sex cell
-gamete has only one set of
chromosomes and is haploid
Cellular Organization of the Genetic Material
• before the cell can divide – it must duplicate its DNA
• REMINDER: eukaryotic chromosomes consist of chromatin, a
complex of DNA and histone proteins
• following replication, the DNA condenses into chromosomes
– starts just prior to Mitosis
every eukaryotic species has a characteristic
number of chromosomes in each cell nucleus
e.g. humans – n=23
e.g. drosophila – n=2
e.g. dog – n=39
20 m
• chromosome = organized structure of DNA and protein
– chroma = color
– soma = body
• DNA is duplicated during the S phase of the cell cycle
• then starts to condense just before mitosis
• each condensed & duplicated chromosome is made of two sister chromatids
– these chromatids will separate during cell division and be partitioned into daughter cells
• chromatids are joined by a structure called a centromere
• highly condensed region of the duplicated chromosome
• role in attaching the duplicated chromosome to the spindle
Sister
chromatids
Centromere
0.5 m
• Mitosis is conventionally
divided into five phases
–
–
–
–
Prophase
Metaphase
Anaphase
Telophase
• Cytokinesis begins during
the latter stages of mitosis
Mitosis
http://www.loci.wisc.edu/outreach/bioclips/CDBio.html
http://faculty.stcc.edu/BIOL102/Lectures/lesson8/mitosis.htm
Prophase:
1. the replicated DNA begins to condense into sister chromatids joined at the
centromere  (duplicated) chromosome
2. the centrioles (replicated at G2) move apart from each other
3. the spindle forms between the centrioles (made of microtubules)
4. the condensing, duplicated chromosomes attach to the spindle (via a kinetochore)
5. the nuclear envelope disintegrates
6. the nucleolus disappears
Spindle – structure that includes the
two centrioles, two asters and the spindle
microtubules than span the cell
Prophase
Kinetochore – region of the centromere where
Fragments
Nonkinetochore
the chromosome attaches to the spindle
of nuclear
microtubules
envelope
Chromatid
Kinetochore
Microtubules
Kinetochore
Kinetochore
Kinetochore
microtubule
Microtubules
Centromere
Metaphase: centrioles are now at opposite ends of the cell and the spindle
is complete
1. the chromosomes move and line up along the equator of the cell =
metaphase plate
Anaphase: shortest of the mitotic phases
1. the sister chromatid separate into daughter chromosomes
-one chromatid/chromosome moves toward one centriole of the cell,
the other the opposite
-pulled apart by the action of the spindle
** At the end of this phase – each end of the cell has equivalent numbers
of chromosomes – same number as the parent cell
Telophase: reverse of Prophase & takes place along with the event Cytokinesis
1. nuclear envelope reforms & two daughter nuclei result
2. the nucleolus reappear
3. the spindle disappears
4. daughter chromosomes uncoil  chromatin
Cytokinesis: division of the cytoplasm into the 2 daughter cells (cytokinesis = cell
motion)
-mitosis can occur with cytokinesis  a single cell with 2 nuclei
-so actual cell division is cytokinesis!!!
-mitosis is actually the division of the nucleus = karyokinesis
-formation of a cleavage furrow that expands
to split the cell into daughters
(a) Cleavage of an animal cell (SEM)
Cleavage furrow
Contractile ring of
microfilaments
100 m
Daughter cells
Plant cell Cytokinesis: No cleavage furrow possible
-vesicles containing parts of the new cell wall form and migrate to the middle of the cell
-vesicles fuse together to produce a cell plate
-cell plate grows and eventually splits the parent into two daughter cells
Cell plate
10 m
(b) Cell plate formation in a plant cell (TEM)
Vesicles
forming
cell plate
5 Telophase
Wall of parent cell
Cell plate
1 m
New cell wall
Daughter cells
Meiosis
• results in four haploid daughter
cells with half the number of
un-replicated chromosomes as
the parental cell
The Stages of Meiosis
• after chromosomes duplicate in
interphase, two divisions follow
– Meiosis I: results in two
haploid daughter cells
containing half the number of
duplicated chromosomes as
the parent
• parent – 46 duplicated
chromosomes
• daughter cell – 23 duplicated
chromosomes
– Meiosis II: results in four
haploid daughter cells
containing single
chromatid/chromosomes
• new “parent cell” – 23
duplicated chromosomes
• daughter cell – 23
chromatid/chromosomes
Interphase
Pair of homologous
chromosomes in
diploid parent cell
Duplicated pair
of homologous
chromosomes
Sister
chromatids
Chromosomes
duplicate
Diploid cell with
duplicated
chromosomes
Meiosis I
1 Homologous
chromosomes separate
Haploid cells with
duplicated chromosomes
Meiosis II
2 Sister chromatids
separate
Haploid cells with unduplicated chromosomes
Anaphase I
Metaphase I
Prophase I
Centrosome
(with centriole pair)
Sister
chromatids
Chiasmata
Spindle
Telophase I and
Cytokinesis
Sister chromatids
remain attached
Centromere
(with kinetochore)
Metaphase
plate
Homologous
chromosomes
Fragments
of nuclear
envelope
Duplicated homologous
chromosomes (red and blue)
pair and exchange segments;
2n  6 in this example.
Homologous
chromosomes
separate
Microtubule
attached to
kinetochore
Each pair of homologous
chromosomes separates.
Chromosomes line up
by homologous pairs.
• Division in meiosis I occurs in four phases:
– Prophase I
– Metaphase I
– Anaphase I
– Telophase I and cytokinesis
Cleavage
furrow
Two haploid
cells form; each
chromosome
still consists
of two sister
chromatids.
Prophase I
• many similarities with mitotic prophase
– chromosomes begin to condense within the nucleus
– the centrioles migrate and the spindle begins to forms
– chromosomes attach to the spindle
• BUT a unique event happens – synapsis = pairing of 2 homologous chromosomes
– the paired chromosomes are called a tetrad
– this pairing is necessary for a special event called crossing over
– crossing over results in the exchange of genetic information between
chromosomes
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__stages_of_meiosis.html
What are homologous chromosomes?
• a set of one maternal chromosome and one paternal chromosome
– e.g. maternal chromosome 1 + paternal chromosome 1
• homologous, duplicated chromosomes pair up with each other inside a cell during
meiosis
Metaphase I
• tetrads line up at the metaphase plate - with one chromosome facing each pole &
the other chromosome facing the other pole
• crossing over takes place during this phase
• alignment is different from mitosis
Metaphase I
Metaphase
Crossing Over
• introduces genetic variability by exchanging genetic information between
homologous chromosomes
Metaphase I
Anaphase I
Metaphase
II
Anaphase II
Gametes
Anaphase I
• the duplicated homologous chromosomes separate
• each duplicated chromosome moves toward each pole - guided by
the spindle apparatus
Prophase II
Metaphase II
Anaphase II
Telophase II and
Cytokinesis
During another round of cell division, the sister chromatids finally separate;
four haploid daughter cells result, containing unduplicated chromosomes.
Haploid daughter
Sister chromatids
cells forming
separate
• Division in meiosis II also occurs in four phases
– Prophase II
– Metaphase II
– Anaphase II
– Telophase II and cytokinesis
• Meiosis II is identical to mitosis