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
Interphase
• Synthesizes new organelles and molecules
• Growth phase
• Chromosomes duplicated
– Not individually distinguishable
– Loosely packed into chromatin
• Contains nucleoli indicating cell is making
proteins
Prophase
• Chromatin fibers more tightly coiled and
folded
– Form discrete chromosomes
– Nucleoli disappear
– Duplicated chromosomes appear and joined at
centromere
• Mitotic spindle forms in cytoplasm
Prometaphase
• Nuclear envelope fragments and disappears
• Microtubules emerge from centrosome at
poles ad reach chromosomes
• Chromosomes tightly condensed
• Kinetochore sppears
Metaphase
• Mitotic spindle formed
• Chromosomes line up at metaphase plate
• Centromeres of chromosomes line up
Anaphase
• Two centromeres of each chromosome come
apart
• Sister chromatids separate
• Poles move farther apart, elongating cell
• Complete collection of chromosomes at each
pole
Telophase and Cytokinesis
• Telophase
– Nucleear envelope reforms
– Chromosomes uncoil into chromatin
– Nucleoli reappear
• Cytokinesis
– Cell divides in two
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
Cytokinesis
• Cleavage
– Starts in telophase or late anaphase
– Cleavage furrow
• Shallow groove on cell surface
• Microfilaments draw together and split cell in two
• Cell wall
– Vesicles containing cell wall material form cell
plate
• Telophase
• Form cell plate that grows out to fuse with existing wall
Cytokenesis
•Cleavage furrow
•Microfilaments
contract
Cleavage
furrow
Cleavage furrow Contracting ring of
microfilaments
Daughter cells
Wall of
parent cell
Cell wall
Cell plate
forming
Daughter
nucleus
New cell wall
Vesicles containing Cell plate Daughter cells
cell wall material
Cell Division
• 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
Growth
• 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
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
– No anchorage dependence
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
