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CH 8
Reproduction and Inheritance
Reproduction
LM 340
• Asexual Reproduction
• Sexual Reproduction
Prokaryotes are asexual
• Via binary fission
– Recall that
Prokaryotes have
circular DNA
Plasma
membrane
Prokaryotic
chromosome
Cell wall
1
Duplication of chromosome
and separation of copies
2
Continued elongation of the
cell and movement of copies
Prokaryotic chromosomes
3
Division into
two daughter cells
Figure 8.3A
LM 600
Eukaryotes
• Complex cell
division
• Chromosomes
occur as chromatin
unless dividing
• Individual
chromosomes
visible when cell is
dividing
Chromosomes
• DNA organizes into chromosomes
– Chromosomes duplicate as cell prepares to divide
– After duplication, each chromosome consists of 2
sister chromatids
• Constricted at centromere
• 23 pair of homologous chromosomes in
humans
Fig. 8-4bc
Sister chromatids
Chromosome
duplication
Centromere
Sister
chromatids
Chromosome
distribution
to
daughter
cells
Mitosis & Meiosis
• Mitosis- nuclear division that maintains
chromosome numbers
• Meiosis- nuclear division that halves the
chromosome number
Cell cycle
• Ordered sequence of events from time a cell is
first formed until its own division
– Growth phase
• Interphase
– Division phase (mitotic phase)
• Mitosis
• Cytokinesis
Fig. 8-5
INTERPHASE
S
(DNA synthesis)
G1
G2
Interphase
• G1
– Cell growth before DNA replication
– Contains nucleoli indicating cell is making proteins
• S
– DNA replication
• G2
– Second stage of growth before division
– Make proteins to drive mitosis
Cell cycle control system
• Set of molecules that triggers and coordinates
key events in cell cycle
– Checkpoints
• Cell is set to STOP until told to GO
• Some cells stuck in “stop”, i.e. nerve cells always in G1
Mitosis
•
•
•
•
•
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Prophase
• Chromatin fibers more tightly coiled and
folded
– Form discrete chromosomes
– Nucleoli disappear
– Duplicated chromosomes appear and joined at
centromere
– Nuclear envelope beings to dissolve
• Centromsomes duplicate and move to
opposite ends of nucleus
– Mitotic spindle forms in cytoplasm
Prophase
Mitotic Spindle
• Centrosome
– Region near the nucleus that organizes microtubules
– Two barrel-shaped centrioles (not found in plant cells)
– Microtubules grow from centrosome to form a spindle
• The spindle attaches to and moves chromosomes
during nuclear division
– Attach to chromosome at kinetochore
– Attach to cell wall
– Add or loose subunits to push and pull chromosomes apart
Prometaphase/Metaphase
• Nuclear envelope fragments and disappears
• Kinetochore visible
• Mitotic spindle formed and microtubules
attach to sister chromatids
• Chromosomes line up at metaphase plate
• Centromeres of chromosomes line up
Fig. 8-6ad
PROMETAPHASE
METAPHASE
Anaphase
• Two centromeres of each chromosome come
apart
– Motor proteins on spindle drag chromatids apart
• Sister chromatids separate
• Poles move farther apart, elongating cell
• Complete collection of chromosomes at each
pole
ANAPHASE
Telophase
• Telophase
– Nuclear envelope reforms
– Chromosomes uncoil into chromatin
– Nucleoli reappear
• Cytokinesis
– Cell divides in two
TELOPHASE
Fig. 8-6a
INTERPHASE
Chromatin
Centrosomes
(with centriole pairs)
PROPHASE
Early mitotic Centrosome
spindle
PROMETAPHASE
Fragments
of nuclear
envelope
Centromere
Plasma
Nuclear
envelope membrane Chromosome, consisting
of two sister chromatids
Nucleolus
Kinetochore
Spindle
microtubules
Fig. 8-6b
METAPHASE
ANAPHASE
Metaphase
plate
Spindle
Daughter
chromosomes
TELOPHASE AND CYTOKINESIS
Cleavage
furrow
Nuclear
envelope
forming
Nucleolus
forming
1) Early Prophase
Mitosis begins. In the nucleus, the DNA
begins to appear grainy as it organizes and
condenses. The centrosome is duplicated.
centrosome
2) Prophase
The chromosomes become visible as distinct structures
as they condense further. Microtubules assemble
and move one of the two centrosomes to the opposite
side of the nucleus, and the nuclear envelope breaks up.
3) Transition to Metaphase
The nuclear envelope is gone, and the chromosomes
are at their most condensed. Spindle microtubules
assemble and attach sister chromatids to opposite
spindle poles.
4) Metaphase
All of the chromosomes are aligned midway between the spindle
poles. Microtubules attach each chromatid to one of the spindle
poles, and its sister to the opposite pole.
pole
pole
microtubule of
spindle
5) Anaphase
Motor proteins moving along spindle microtubules drag the
chromatids toward the spindle poles, and the sister chromatids
separate. Each sister chromatid is now a separate chromosome.
6) Telophase
The chromosomes reach the spindle poles and decondense. A
nuclear envelope forms around each cluster. Mitosis is over.
Stepped Art
Fig. 8-5b (6), p. 141
Cytokinesis
• Cleavage- Animal cells
– Starts in telophase or late anaphase
– Cleavage furrow
• Shallow groove on cell formed via contractile ring
• Microfilaments draw together and split cell in two
• Cell wall
– Vesicles containing cell wall material form cell
plate
• Form cell plate that grows out to fuse with existing wall
Cytokinesis
Wall of
parent cell
Cytokenesis
Cell plate
forming
Cleavage furrow
Cleavage
furrow
Cell wall
New cell wall
Vesicles containing Cell plate
cell wall material
Contracting ring of
microfilaments
Daughter cells
Daughter cells
Cell Division Control
• Growth factors
– Proteins that stimulate cell to divide
• Density-Dependent inhibition
– Stop cells from dividing under crowded conditions
• Anchorage dependence
– Need surface on which to divide
Control
Cell cycle control
system
Set of
molecules
that triggers
and
coordinates
key events in
cell cycle
G1 checkpoint
G0
Control
system
G1
M
G2
M checkpoint
G2 checkpoint
S
Fig. 8-9b
Growth factor
Plasma membrane
Receptor
protein
Signal
transduction
pathway
Relay
proteins
G1 checkpoint
Control
system
G1
M
G2
S
Out of control
• Cancer
– Do not respond to cell control system
– No density-dependent inhibition
– Divide indefinitely
– No anchorage dependence
Meiosis terms
• Somatic cells- non-reproductive cells
• Gametes- reproductive cells (sex cells)
• Homologous chromosomes- chromosomes
with same genes at same loci
• Sex chromosomes- determine sex
• Autosomes- non-sex chromosomes
• Diploid- 2 sets of chromosomes
• Haploid- single set of chromosomes
• Alleles- different forms of the same gene
Fig. 8-13
Haploid gametes (n = 23)
n
Egg cell
n
Sperm cell
Meiosis
Fertilization
Diploid
zygote
(2n = 46)
Multicellular
diploid adults
(2n = 46)
Mitosis and
development
2n
Meiosis
• Produces haploid gametes in diploid
organisms
• Duplication of chromosomes
– Two cell divisions
– Form a tetrad
Crossing over
• A chromosome and its homologous partner
exchange a corresponding piece of DNA
crossover
Fig. 8-10a, p. 146
Fig. 8-10b, p. 147
Fig. 8-15
MITOSIS
MEIOSIS
Parent cell
(before chromosome duplication)
Site of
crossing over
MEIOSIS I
Prophase I
Prophase
Duplicated
chromosome
(two sister
chromatids)
Tetrad formed
by synapsis of
homologous
chromosomes
Chromosome
duplication
Chromosome
duplication
2n = 4
Chromosomes
align at the
metaphase plate
Metaphase
Anaphase
Telophase
Sister chromatids
separate during
anaphase
2n
2n
Daughter cells
of mitosis
Tetrads
align at the
metaphase plate
Homologous
chromosomes
separate
(anaphase I);
sister chromatids remain
together
No further
chromosomal
duplication;
sister
chromatids
separate
(anaphase II)
Metaphase I
Anaphase I
Telophase I
Haploid
n=2
Daughter
cells of
meiosis I
MEIOSIS II
n
n
n
n
Daughter cells of meiosis II
Diversity
• Random arrangement of homologous
chromosomes
• Different gene versions
• Genetic recombination
– “Crossing over”
Error
•Abnormal sex
chromosomes
Nondisjunction
in meiosis I
•Trisomy 21
Normal
meiosis II
Gametes
n+1
n+1
n–1
Number of chromosomes
n–1
Error
• Down syndrome
– Extra copy of
chromosome 21
Videos
• Overview
– http://www.youtube.com/watch?v=3kpR5RSJ7SA&feature
=related
– http://www.youtube.com/watch?v=s4PaOz7eWS8&featur
e=related
• Cytokinesis
– http://www.youtube.com/watch?v=mzeowbIxgwI
• Meiosis
– http://www.youtube.com/watch?v=D1_mQS_FZ0&feature=related
– http://www.youtube.com/watch?v=3xtD8uUZBhM&featur
e=related
Videos
• Mutations and DNA
• http://www.youtube.com/user/greatpacificm
edia#p/u/43/hkK5hDbxJ0M