Download Mitosis & Meiosis Ch11

Cellular Reproduction
• Cell
division in
eukaryotes
enables
asexual
reproduction
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(F11.1 p. 186)
Cellular Reproduction
cell
division
Prokaryotic
Cell Cycle:
Growth &
Binary Fission
(F11.2 p187)
attachment
site
cell
wall
plasma
membrane
cell growth and
DNA replication
circular
DNA
The circular DNA double helix is attached
to the plasma membrane at one point.
The parent cell divides into two
daughter cells.
The DNA replicates and the two
DNA double helices attach to the
plasma membrane at nearby points.
New plasma membrane is added
between the attachment points,
pushing them further apart.
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The plasma membrane grows inward
at the middle of the cell.
Cellular
Reproduction
telophase and
cytokinesis
G1: cell growth and
differentiation
G0: nondividing
G2: cell
growth
Eukaryotic
Cell Cycle:
•Interphase
•Cell
Division
p. Pearson
188)
Copyright (F11.3
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interphase
S: synthesis
of DNA;
chromosomes
are duplicated
Interphase:
Cell Grows in
Size
Replicates Its
DNA
DNA in Eukaryotic Cells Is
Organized into Chromosomes
• Eukaryotic Chromosome = 1 Linear DNA Double
Helix Bound to Proteins
–
–
–
–
Chromosome structure
Human chromosomes during mitosis
(Duplicated) REPLICATED chromosome
Daughter chromosomes
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(F11.5 p. 190)
(F11.6 p. 191)
(F2 p. 191)
(F3 p. 191)
DNA (2 nm diameter)
histone proteins
nucleosome: DNA wrapped around
histone proteins
(10 nm diameter)
coiled nucleosomes
(30 nm diameter)
chromosome:
coils gathered onto
protein
protein scaffold
scaffold
(200 nm diameter)
DNA coils
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sister chromatids
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centromere
genes
centromere
telomeres
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independent
daughter
chromosomes,
each with one
identical DNA
double helix
sister
chromatids
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duplicated
chromosome
(2 DNA
double
helices)
DNA in Eukaryotic Cells Is
Organized into Chromosomes
• Eukaryotic Chromosomes:
– Usually Occur in Homologous Pairs
• 1 from Mom & 1 from Dad
– Homologs Have Similar (NOT IDENTICAL)
Genetic Information
• Some from Mom & Some from Dad
– Karyotype of a human male
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(F11.7 p. 191)
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Cellular Reproduction
• Two Types of Eukaryotic Cell Division :
– Mitotic Cell Division
– Meiotic Cell Division
• Figure 11.4 (Hide/Reveal) Mitotic and meiotic
cell division in the human life cycle (p. 189)
• Unnumbered Figure 1 Chromosome (p. 190)
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Mitotic Cell Division
• Mitotic cell division in an animal cell
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(F11.8 p. 192)
INTERPHASE
nuclear
envelope
MITOSIS
chromatin
nucleolus
centriole
pairs
LATE INTERPHASE
Duplicated chromosomes in
relaxed state; duplicated
centrioles remain clustered.
condensing
chromosomes
pole
beginning of
spindle formation pole
EARLY PROPHASE
Chromosomes condense
and shorten; spindle
microtubules begin to
form between separating
centriole pairs.
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spindle
microtubules
kinetochore
LATE PROPHASE
Nucleolus disappears;
nuclear envelope breaks
down; spindle microtubules
attach to the kinetochore
of each sister chromatid.
METAPHASE
Kinetochores interact;
spindle microtubules line
up chromosomes at cell's
equator.
"free" spindle
fibers
chromosomes
extending
ANAPHASE
Sister chromatids separate
and move to opposite poles
of the cell; spindle
microtubules push poles
apart.
INTERPHASE
nuclear envelope
re-forming
TELOPHASE
One set of chromosomes
reaches each pole and relaxes
into extended state; nuclear
envelopes start to form
around each set; spindle
microtubules begin to
disappear.
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CYTOKINESIS
Cell divides in two; each
daughter cell receives one
nucleus and about half of
the cytoplasm.
INTERPHASE OF
DAUGHTER CELLS
Spindles disappear, intact
nuclear envelopes form,
chromosomes extend
completely, and the
nucleolus reappears.
Finn Dorset ewe
donor cell
from udder
electric pulsefused cells
Cells from the udder of a Finn Dorset ewe
are grown in culture with low nutrient levels.
The starved cells stop dividing and enter the
non-dividing G0 phase of the cell cycle.
Blackface ewe
egg
cell
Meanwhile, the nucleus is
sucked out of an unfertilized egg
cell taken from a Scottish Blackface
ewe. This egg will provide cytoplasm
and organelles but no chromosomes.
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nucleus is
removed
DNA
The egg cell without a
nucleus and the quiescent
udder cell are placed side by
side in a culture dish. An
electric pulse stimulates the
cells to fuse and initiates mitot
cell division.
The cell divides, forming an
embryo that consists of a hollow
ball of cells.
The ball of cells is implanted
The Blackface ewe gives
into the uterus of another
birth to Dolly, a female
Blackface ewe.
Finn Dorset lamb, a
genetic twin of the Finn
Dorset ewe.
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Mitotic Cell Division
• Prophase
– Chromosomes Condense, Spindle Microtubules Form &
Attach to the Chromosomes
• Metaphase
– Chromosomes Align Along the Equator of the Cell
• Anaphase
– Sister Chromatids Separate & Pulled to Opposite Poles of
the Cell
• Telophase
– Nuclear Envelopes Form Around Both Groups of
Chromosomes
• Cytokinesis
– Cytoplasm Is Divided Between Two Daughter Cells
– Cytokinesis in an animal cell
(F11.9 p. 197)
– Cytokinesis in a plant cell
(F11.10 p. 197)
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Microfilaments form
a ring around the cell's
equator.
The microfilament ring
contracts, pinching
in the cell's “waist.”
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The waist completely
pinches off, forming
two daughter cells.
Golgi complex
cell wall
plasma
membrane
carbohydratefilled vesicles
Carbohydratefilled vesicles bud off
the Golgi complex and
move to the equator of
the cell.
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Vesicles fuse to form
a new cell wall (red) and
plasma membrane
(yellow) between
daughter cells.
Complete
separation of
daughter cells.
Cellular Reproduction
• Two Types of Eukaryotic Cell Division :
– Mitotic Cell Division
– Meiotic Cell Division
• Mitotic & meiotic cell division in human life cycle
(F11.4 p. 189)
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mitosis,
differentiation, and growth
mitosis,
differentiation,
and growth
baby
meiosis in
ovaries
embryo
mitosis,
differentiation,
and growth
adults
egg
fertilized
egg
fertilization
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sperm
meiosis in
testes
gene 1
same alleles
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gene 2
different allele
sister
chromatids
homologous
chromosomes
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Prentice©Hall,
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2005 Pearson Prentice Hall,
Meiotic Cell Division
Produces Haploid Cells
• Meiosis Separates Homologous Chromosomes, Producing Haploid
Daughter Nuclei
• Meiotic Cell Division Followed by Fusion of Gametes Keeps the
Chromosome Number Constant from Generation to Generation
• Meiosis I Separates Homologous Chromosomes into Two Haploid
Daughter Nuclei
– During Prophase I, Homologous Chromosomes Pair Up and Exchange DNA
• Homologous chromosomes
(F5 p. 198)
•
•
•
•
Two daughter nuclei
Four haploid cells
Meiotic cell division
Meiotic cell division in an animal cell
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(F6 p. 198)
(F 7 p. 199)
(F8 p. 199)
(F11.11 p. 200)
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n
2n
meiotic
cell division
2n
2n
n
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fertilization
MEIOSIS I
paired homologous
chromosomes
chiasma
recombined
chromosomes
spindle
microtubule
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MEIOSIS I
paired homologous
chromosomes
chiasma
recombined
chromosomes
spindle
microtubule
Prophase I. Duplicated
chromosomes condense.
Homologous chromosomes
pair up and chiasmata occur
as chromatids of homologues
exchange parts. The nuclear
envelope disintegrates, and
spindle microtubules form.
Metaphase I. Paired
homologous chromosomes
line up along the equator of
the cell. One homologue of
each pair faces each pole
of the cell and attaches to
spindle microtubules via its
kinetochore (blue).
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Anaphase I. Homologues
separate, one member of
each pair going to each pole
of the cell. Sister chromatids
do not separate.
Telophase I. Spindle
microtubules disappear. Two
clusters of chromosomes have
formed, each containing one
member of each pair of
homologues. The daughter nuclei
are therefore haploid. Cytokines
commonly occurs at this stage.
There is little or no interphase
between meiosis I and meiosis II
MEIOSIS II
Prophase II.
If chromosomes
have relaxed after
telophase I, they
recondense. Spindle
microtubules re-form
and attach to the
sister chromatids.
Metaphase II.
Chromosomes line
up along the equator,
with sister chromatids
of each chromosome
attached to spindle
microtubules that lead
to opposite poles.
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Anaphase II.
Chromatids separate
into independent
daughter chromosomes,
one former chromatid
moving toward each
pole.
Telophase II.
Chromosomes finish
moving to opposite
poles. Nuclear
envelopes re-form,
and the chromosomes
become extended
again (not shown here).
Four haploid
cells.
Cytokinesis results in
four haploid cells,
each containing one
member of each pair
of homologous
chromosomes (shown
here in condensed
state).
Meiotic Cell Division
Produces Haploid Cells
• Meiosis I
–
–
–
–
Metaphase I, Paired Homologs Line Up at the Equator of the Cell
Anaphase I, Homologs Separate
Telophase I, Two Haploid Clusters of Duplicated Chromosomes Form
Mitosis, Meiosis I
(F9, 10 p. 202)
• Meiosis II Separates Sister Chromatids into Four Daughter Nuclei
– The mechanism of crossing over
(F11.12p. 200)
– Comparison of Animal Cell Mitotic & Meiotic Cell Divisions (T11.1 p. 203)
– Chromosome configurations at metaphase I
F11
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sister
chromatids of
one duplicated
homologue
protein strands
joining duplicated
chromosomes
direction of
“zipper”
formation
pair of homologous,
duplicated chromosomes
Duplicated homologous
chromosomes pair up side
by side.
recombinatio
n
enzymes
Protein strands “zip” the
homologous chromosomes
together.
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Recombination
enzymes bind to the
joined chromosomes.
chiasma
Recombination
enzymes snip
chromatids apart
and reattach the
free ends.
Chiasmata (the
sites of crossing
over) form when
one end of the
paternal chromatid
(yellow) attaches
to the other end
of a maternal
chromatid
(purple).
chiasma
Recombination enzymes
and protein zippers leave.
Chiasmata remain, helping
to hold homologous
chromosomes together.
duplicated
chromosomes
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spindle
microtubules
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Why Do So Many Organisms
Reproduce Sexually?
• Mutations in DNA Are the Ultimate
Source of Genetic Variability
• Sexual Reproduction May Combine
Different Parental Alleles in a Single
Offspring
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How Do Meiosis & Sexual
Reproduction Produce Genetic
Variability?
• Shuffling of Homologues Creates Novel
Combinations of Chromosomes
• Crossing Over Creates Chromosomes with
Novel Combinations of Genes
• Fusion of Gametes Adds Further Genetic
Variability to the Offspring
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duplicated
chromosomes
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spindle
microtubules
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