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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
Cell cycle
• Ordered sequence of events from time a cell is
first formed until its own division
• Growth phase
• Division phase (mitotic phase)
– Mitosis
– Cytokinesis
Fig. 8-5
INTERPHASE
S
(DNA synthesis)
G1
G2
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
Cytokenesis
•Cleavage furrow
•Microfilaments
contract
Cleavage
furrow
Cleavage furrow Contracting ring of
microfilaments
Daughter cells
Wall of
parent cell
Cell plate
forming
Daughter
nucleus
Plant cells
Cell plate
Cell wall
New cell wall
Vesicles containing Cell plate Daughter cells
cell wall material
Cell Division
• Growth factors
• Density-Dependent inhibition
• Anchorage dependence
Growth
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
Meiosis terms
•
•
•
•
•
•
Somatic cells
Homologous chromosomes
Sex chromosomes
Autosomes
Diploid
Haploid
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
Fig. 8-14a
MEIOSIS I: Homologous chromosomes separate
INTERPHASE
Centrosomes
(with centriole
pairs)
Nuclear
envelope
PROPHASE I
METAPHASE I
ANAPHASE I
Microtubules Metaphase Sister chromatids
remain attached
plate
attached to
Spindle kinetochore
Sites of crossing over
Sister
Chromatin chromatids
Tetrad
Centromere
(with kinetochore)
Homologous
chromosomes separate
Fig. 8-14b
MEIOSIS II: Sister chromatids separate
TELOPHASE II
AND CYTOKINESIS
PROPHASE I
METAPHASE II
ANAPHASE II
TELOPHASE II
AND CYTOKINESIS
Sister chromatids
separate
Haploid daughter
cells forming
Cleavage
furrow
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