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Chapter 47: Animal Development
1. What exactly happens when sperm meets egg?
Figure 47.3 The acrosomal and cortical reactions during sea
urchin fertilization
1 Contact. The
sperm cell
contacts the
egg’s jelly coat,
triggering
exocytosis from the
sperm’s acrosome.
2 Acrosomal reaction. Hydrolytic
enzymes released from the
acrosome make a hole in the
jelly coat, while growing actin
filaments form the acrosomal
process. This structure protrudes
from the sperm head and
penetrates the jelly coat, binding
to receptors in the egg cell
membrane that extend through
the vitelline layer.
3 Contact and fusion of sperm
and egg membranes. A hole
is made in the vitelline layer,
allowing contact and fusion of
the gamete plasma membranes.
The membrane becomes
depolarized, resulting in the
fast block to polyspermy.
4 Entry of
sperm nucleus.
Sperm plasma
membrane
5 Cortical reaction. Fusion of the
gamete membranes triggers an
increase of Ca2+ in the egg’s
cytosol, causing cortical granules
in the egg to fuse with the plasma
membrane and discharge their
contents. This leads to swelling of the
perivitelline space, hardening of the
vitelline layer, and clipping of
sperm-binding receptors. The resulting
fertilization envelope is the slow block
to polyspermy.
Sperm
nucleus
Acrosomal
process
Basal body
(centriole)
Fertilization
envelope
Sperm
head
Actin
Acrosome
Jelly coat
Sperm-binding
receptors
Fused plasma
Cortical membranes
granule
Perivitelline
Hydrolytic enzymes
space
Cortical granule
membrane
Vitelline layer
Egg plasma
membrane
EGG CYTOPLASM
Chapter 47: Animal Development
1. What exactly happens when sperm meets egg?
1. Contact – acrosome releases hydrolytic enzymes
2. Acrosomal rxn – enzymes digest jelly coat while actin extends
- acrosomal process attaches to sperm binding receptors
3. Membrane fusion (sperm & egg) – causes depolarization as Ca+2 released
- aka fast block to polyspermy
- aka activation of the egg begins
4. Sperm nucleus enters egg
5. Cortical rxn – cortical granules from egg fuse with plasma membrane
- Forms fertilization envelope aka slow block to polyspermy
2. What happens with activation of the egg?
- Ca+2 released from ER
- ↑ Cellular respiration & ↑ protein synthesis (translation)
Figure 47.4 What is the effect of sperm binding on Ca2+ distribution
in the egg?
EXPERIMENT
A fluorescent dye that glows when it binds free Ca2+ was injected into unfertilized sea urchin eggs. After sea urchin
sperm were added, researchers observed the eggs in a fluorescence microscope.
500 m
RESULTS
1 sec before
fertilization
10 sec after
fertilization
Point of
Sperm
entry
20 sec
30 sec
Spreading wave
of calcium ions
CONCLUSION The release of Ca2+ from the endoplasmic reticulum into the cytosol at the site of sperm entry triggers the release
of more and more Ca2+ in a wave that spreads to the other side of the cell. The entire process takes about 30 seconds.
Figure 47.5 Timeline for the fertilization of sea urchin eggs
1
Binding of sperm to egg
2
Acrosomal reaction: plasma membrane
depolarization (fast block to polyspermy)
3
4
6
8
10
Increased intracellular calcium level
20
Cortical reaction begins (slow block to polyspermy)
30
40
50
1
Formation of fertilization envelope complete
2
Increased intracellular pH
3
4
5
Increased protein synthesis
10
20
Fusion of egg and sperm nuclei complete
30
40
Onset of DNA synthesis
60
90
First cell division
Chapter 47: Animal Development
1. What exactly happens when sperm meets egg?
2. What happens with activation of the egg?
3. What happens in mammals?
Figure 47.6 Early events of fertilization in mammals
1 The sperm migrates
through the coat of
follicle cells and
binds to receptor
molecules in the
zona pellucida of
the egg. (Receptor
molecules are not
shown here.)
2 This binding induces
the acrosomal reaction,
in which the sperm
releases hydrolytic
enzymes into the
zona pellucida.
3 Breakdown of the zona pellucida
by these enzymes allows the sperm
to reach the plasma membrane
of the egg. Membrane proteins of the
sperm bind to receptors on the egg
membrane, and the two membranes fuse.
4 The nucleus and other
components of the sperm
cell enter the egg.
Follicle
cell
5 Enzymes released during
the cortical reaction harden
the zona pellucida, which
now functions as a block to
polyspermy.
Zone
pellucida
Egg plasma
membrane
Sperm
basal
body
Cortical
Sperm
granules
nucleus
Acrosomal
vesicle
EGG CYTOPLASM
Chapter 47: Animal Development
1. What exactly happens when sperm meets egg?
2. What happens with activation of the egg?
3. What happens in mammals?
1. Contact – sperm migrates through follicle cells & binds to zona pellucida
2. Acrosomal rxn – acrosome releases hydrolytic enzymes digesting ZP
3. Sperm bind to sperm receptors on 2° oocyte & membranes fuse
4. Sperm nucleus enters egg
5. Cortical reaction hardens ZP as a block to polyspermy
4. What happens with during cleavage?
1. Cell division w/o cytokinesis
2. Creates blastomeres
3. Axes formed at first cleavage in amphibians
Figure 47.8 The body axes and their establishment in an amphibian
Anterior
(a) Body axes. The three axes of the fully developed embryo, the
tadpole, are shown above.
Right
Ventral
Dorsal
Left
1 The polarity of the egg determines the anterior-posterior axis
before fertilization.
Posterior
Animal
hemisphere
Animal pole
Point of
sperm entry
Vegetal
hemisphere
2 At fertilization, the pigmented cortex slides over the underlying
cytoplasm toward the point of sperm entry. This rotation (red arrow)
exposes a region of lighter-colored cytoplasm, the gray crescent,
which is a marker of the dorsal side.
3 The first cleavage division bisects the gray crescent. Once the anteriorposterior and dorsal-ventral axes are defined, so is the left-right axis.
Point of
sperm
entry
Gray
crescent
Vegetal pole
Future
dorsal
side of
tadpole
First
cleavage
(b) Establishing the axes. The polarity of the egg and cortical rotation are critical in setting up the body axes.
Figure 47.9 Cleavage in a frog embryo
Zygote
0.25 mm
2-cell
stage
forming
Eight-cell stage (viewed from the animal pole). The large
amount of yolk displaces the third cleavage toward the animal pole,
forming two tiers of cells. The four cells near the animal pole
(closer, in this view) are smaller than the other four cells (SEM).
4-cell
stage
forming
8-cell
stage
0.25 mm
Animal pole
Blastula
(cross
section)
Vegetal pole
Blastocoel
Blastula (at least 128 cells). As cleavage continues, a fluid-filled
cavity, the blastocoel, forms within the embryo. Because of unequal
cell division due to the large amount of yolk in the vegetal
hemisphere, the blastocoel is located in the animal hemisphere, as
shown in the cross section. The SEM shows the outside of a
blastula with about 4,000 cells, looking at the animal pole.
Chapter 47: Animal Development
1.
2.
3.
4.
5.
What exactly happens when sperm meets egg?
What happens with activation of the egg?
What happens in mammals?
What happens with during cleavage?
What is gastrulation?
- Movement of blastula cells into the blastopore creating 2 cell (germ) layers
- Ectoderm – outer layer
- Endoderm – inner layer
- Mesoderm – forms in between
Figure 47.12 Gastrulation in a frog embryo
1 Gastrulation begins when a small indented crease,
the dorsal lip of the blastopore, appears on one
side of the blastula. The crease is formed by cells
changing shape and pushing inward from the
surface (invagination). Additional cells then roll
inward over the dorsal lip (involution) and move into
the interior, where they will form endoderm and
mesoderm. Meanwhile, cells of the animal pole, the
future ectoderm, change shape and begin spreading
over the outer surface.
SURFACE VIEW
Animal pole
CROSS SECTION
Blastocoel
Dorsal lip
Dorsal lip
Vegetal pole of blastopore Blastula of blastopore
Blastocoel
shrinking
2 The blastopore lip grows on both sides of the
embryo, as more cells invaginate. When the sides
of the lip meet, the blastopore forms a circle that
becomes smaller as ectoderm spreads downward
over the surface. Internally, continued involution
expands the endoderm and mesoderm, and the
archenteron begins to form; as a result, the
blastocoel becomes smaller.
3 Late in gastrulation, the endoderm-lined archenteron
has completely replaced the blastocoel and the
three germ layers are in place. The circular blastopore
surrounds a plug of yolk-filled cells.
Blastocoel
remnant
Archenteron
Ectoderm
Mesoderm
Endoderm
Key
Future ectoderm
Future mesoderm
Future endoderm
Yolk plug
Yolk plug
Gastrula
Chapter 47: Animal Development
1.
2.
3.
4.
5.
6.
What exactly happens when sperm meets egg?
What happens with activation of the egg?
What happens in mammals?
What happens with during cleavage?
What is gastrulation?
What is organogenesis?
- Creation of organs
- Involves folds, splits & clustering of cells
- 1st organs are neural tube & notocord
Chapter 47: Animal Development
Students
Correlations available now – sorry for the delay 
Learning Log – later today
AP checks?? – March 9 deadline
Has anyone not taken the Biology EOC? Transfers, movers,
Figure 47.14 Early organogenesis in a frog embryo
Neural folds
Eye
Neural
fold
Tail bud
Neural plate
SEM
LM
Somites
Neural tube
1 mm
1 mm
Neural
fold
Notochord
Neural
plate
Neural crest
Coelom
Neural
crest
Somite
Notochord
Ectoderm
Mesoderm
Outer layer
of ectoderm
Endoderm
Archenteron
Neural crest
(a) Neural plate formation. By the time
shown here, the notochord has
developed from dorsal mesoderm,
and the dorsal ectoderm has
thickened, forming the neural plate,
in response to signals from the
notochord. The neural folds are
the two ridges that form the lateral
edges of the neural plate. These
are visible in the light micrograph
of a whole embryo.
Archenteron
(digestive cavity)
Neural tube
(b) Formation of the neural tube.
Infolding and pinching off of the
neural plate generates the neural tube.
Note the neural crest cells, which will
migrate and give rise to numerous
structures.
(c) Somites. The drawing shows an embryo
after completion of the neural tube. By
this time, the lateral mesoderm has
begun to separate into the two tissue
layers that line the coelom; the somites,
formed from mesoderm, flank the
notochord. In the scanning electron
micrograph, a side view of a whole
embryo at the tail-bud stage, part of the
ectoderm has been removed, revealing
the somites, which will give rise to
segmental structures such as vertebrae
and skeletal muscle.
Figure 47.16 Adult derivatives of the three embryonic germ layers
in vertebrates
ECTODERM
• Epidermis of skin and its
derivatives (including sweat
glands, hair follicles)
• Epithelial lining of mouth
and rectum
• Sense receptors in
epidermis
• Cornea and lens of eye
• Nervous system
• Adrenal medulla
• Tooth enamel
• Epithelium or pineal and
pituitary glands
MESODERM
• Notochord
• Skeletal system
• Muscular system
• Muscular layer of
stomach, intestine, etc.
• Excretory system
• Circulatory and lymphatic
systems
• Reproductive system
(except germ cells)
• Dermis of skin
• Lining of body cavity
• Adrenal cortex
ENDODERM
• Epithelial lining of
digestive tract
• Epithelial lining of
respiratory system
• Lining of urethra, urinary
bladder, and reproductive
system
• Liver
• Pancreas
• Thymus
• Thyroid and parathyroid
glands
Chapter 47: Animal Development
1.
2.
3.
4.
5.
6.
7.
What exactly happens when sperm meets egg?
What happens with activation of the egg?
What happens in mammals?
What happens with during cleavage?
What is gastrulation?
What is organogenesis?
What are the 4 extra-embryonic membranes in the amniotic egg?
- Amnion
- Allantois
- Chorion
- Yolk sac
Figure 47.17 Extraembryonic membranes in birds and other reptiles
Amnion. The amnion protects
the embryo in a fluid-filled
cavity that prevents
dehydration and cushions
mechanical shock.
Allantois. The allantois
functions as a disposal sac for
certain metabolic wastes
produced by the embryo. The
membrane of the allantois
also functions with the
chorion as a respiratory organ.
Embryo
Albumen
Amniotic
cavity
with
amniotic
fluid
Shell
Chorion. The chorion and the
membrane of the allantois
exchange gases between the
embryo and the surrounding
air. Oxygen and carbon dioxide
diffuse freely across the egg’s
shell.
Yolk
(nutrients)
Yolk sac. The yolk sac expands
over the yolk, a stockpile of
nutrients stored in the egg.
Blood vessels in the yolk sac
membrane transport nutrients
from the yolk into the embryo.
Other nutrients are stored in
the albumen (the ”egg white”).
Chapter 47: Animal Development
1.
2.
3.
4.
5.
6.
7.
8.
What exactly happens when sperm meets egg?
What happens with activation of the egg?
What happens in mammals?
What happens with during cleavage?
What is gastrulation?
What is organogenesis?
What are the 4 extra-embryonic membranes in the amniotic egg?
How does mammalian development occur?
- Slow cleavage
- 1st division – 36 hrs
- 2nd – 60 hrs
- 3rd – 72 hrs
Figure 47.18 Four stages in early embryonic development of a human
Endometrium
(uterine lining)
Inner cell mass
Trophoblast
Blastocoel
1 Blastocyst
reaches uterus.
Maternal
blood
vessel
Expanding
region of
trophoblast
Epiblast
Hypoblast
Trophoblast
2 Blastocyst
implants.
Expanding
region of
trophoblast
Amnion
Amniotic
cavity
Epiblast
Hypoblast
3 Extraembryonic
membranes
start to form and
gastrulation begins.
Chorion (from
trophoblast)
Extraembryonic mesoderm cells
(from epiblast)
Allantois
Yolk sac (from
hypoblast)
Amnion
Chorion
Ectoderm
Mesoderm
Endoderm
4 Gastrulation has produced a threelayered embryo with four
extraembryonic membranes.
Yolk sac
Extraembryonic
mesoderm
Chapter 47: Animal Development
1.
2.
3.
4.
5.
6.
7.
8.
9.
What exactly happens when sperm meets egg?
What happens with activation of the egg?
What happens in mammals?
What happens with during cleavage?
What is gastrulation?
What is organogenesis?
What are the 4 extra-embryonic membranes in the amniotic egg?
How does mammalian development occur?
What three things influence cell fate?
- Cytoplasmic determinants – mRNA & proteins in egg cytoplasm
- Induction – cellular peer pressure
- Cleavage pattern – divides cytoplasmic determinants
Figure 21.11 Sources of developmental information for the early embryo
Unfertilized egg cell
Sperm
Molecules of a
a cytoplasmic
determinant
Molecules of
another cytoplasmic determinant
Fertilization
Nucleus
Zygote
(fertilized egg)
Mitotic cell division
Two-celled
embryo
(a) Cytoplasmic determinants in the egg. The unfertilized egg cell has molecules in its cytoplasm,
encoded by the mother’s genes, that influence development. Many of these cytoplasmic
determinants, like the two shown here, are unevenly distributed in the egg. After fertilization
and mitotic division, the cell nuclei of the embryo are exposed to different sets of cytoplasmic
determinants and, as a result, express different genes.
Figure 21.11b
Early embryo
(32 cells)
NUCLEUS
Signal
transduction
pathway
Signal
receptor
Signal
molecule
(inducer)
(b) Induction by nearby cells. The cells at the bottom of the early embryo depicted here are releasing
chemicals that signal nearby cells to change their gene expression.
Cellular peer pressure
Figure 47.24 How does distribution of the gray crescent at the first
cleavage affect the potency of the two daughter cells?
EXPERIMENT
1
Gray
crescent
Left (control):
Fertilized
salamander eggs
were allowed to
divide normally,
resulting in the
gray crescent being
evenly divided
between the two
blastomeres.
Right (experimental):
Fertilized eggs were
constricted by a
thread so that the
first cleavage plane
restricted the gray
crescent to one
blastomere.
Gray
crescent
2 The two blastomeres were
then separated and
allowed to develop.
Normal
Belly
piece
Normal
RESULTS
Blastomeres that receive half or all of the gray crescent develop into normal embryos, but a blastomere
that receives none of the gray crescent gives rise to an abnormal embryo without dorsal structures. Spemann called it a
“belly piece.”
CONCLUSION
The totipotency of the two blastomeres normally formed during the first cleavage division depends on
cytoplasmic determinants localized in the gray crescent.
Figure 47.25 Can the dorsal lip of the blastopore induce cells in another
part of the amphibian embryo to change their developmental fate?
EXPERIMENT Spemann and Mangold transplanted a piece of the dorsal lip of a pigmented newt gastrula to the
ventral side of the early gastrula of a nonpigmented newt.
Pigmented gastrula
(donor embryo)
Dorsal lip of
blastopore
Nonpigmented gastrula
(recipient embryo)
RESULTS
During subsequent development, the recipient embryo formed a second notochord and neural tube in
the region of the transplant, and eventually most of a second embryo. Examination of the interior of the double embryo
revealed that the secondary structures were formed in part from host tissue.
Primary embryo
Secondary
structures:
Notochord (pigmented cells)
Neural tube (mostly nonpigmented cells)
Primary
structures: Secondary (induced) embryo
Neural tube
Notochord
CONCLUSION The transplanted dorsal lip was able to induce cells in a different region of the recipient to form
structures different from their normal fate. In effect, the dorsal lip “organized” the later development of an entire embryo.
Chapter 47: Animal Development
1. What exactly happens when sperm meets egg?
2. What happens with activation of the egg?
3. What happens in mammals?
4. What happens with during cleavage?
5. What is gastrulation?
6. What is organogenesis?
7. What are the 4 extra-embryonic membranes in the amniotic egg?
8. How does mammalian development occur?
9. What three things influence cell fate?
10. How are organisms formed from the fertilized egg?
- Cell division/cleavage
- Morphogenesis – process of giving shape to an organism
- Cell differentiation – process by which cells become specialized
Figure 21.4 Some key stages of development in animals and plants
(a) Animal development. Most
animals go through some
variation of the blastula and
gastrula stages. The blastula is
a sphere of cells surrounding a
fluid-filled cavity. The gastrula
forms when a region of the blastula
folds inward, creating a
tube—a rudimentary gut. Once
the animal is mature,
differentiation occurs in only a
limited way—for the replacement
of damaged or lost cells.
Cell
movement
Zygote
(fertilized egg)
Eight cells
Blastula
(cross section)
Gut
Gastrula
Adult animal
(cross section)
(sea star)
Cell division
Morphogenesis
(b) Plant development. In plants
with seeds, a complete embryo
develops within the seed.
Morphogenesis, which involves
cell division and cell wall
expansion rather than cell or
tissue movement, occurs
throughout the plant’s lifetime.
Apical meristems (purple)
continuously arise and develop
into the various plant organs as
the plant grows to an
indeterminate size.
Observable cell differentiation
Seed
leaves
Shoot
apical
meristem
Zygote
(fertilized egg)
Root
apical
meristem
Two cells
Embryo
inside seed
Plant
Chapter 47: Animal Development
1. What exactly happens when sperm meets egg?
2. What happens with activation of the egg?
3. What happens in mammals?
4. What happens with during cleavage?
5. What is gastrulation?
6. What is organogenesis?
7. What are the 4 extra-embryonic membranes in the amniotic egg?
8. How does mammalian development occur?
9. What three things influence cell fate?
10. How are organisms formed from the fertilized egg?
11. Can cells de-differentiate?
- Plant cuttings
- Animal cells????
Figure 21.6 Can the nucleus from a differentiated animal cell
direct development of an organism?
EXPERIMENT Researchers enucleated frog egg cells by exposing them to ultraviolet light, which
destroyed the nucleus. Nuclei from cells of embryos up to the tadpole stage were transplanted into the
enucleated egg cells.
Frog embryo
Frog egg cell
Fully differentiated
(intestinal) cell
Less differentiated cell
Donor
nucleus
transplanted
Most develop
into tadpoles
Frog tadpole
Enucleated
egg cell
Donor
nucleus
transplanted
<2% develop
into tadpoles
Chapter 47: Animal Development
1. What exactly happens when sperm meets egg?
2. What happens with activation of the egg?
3. What happens in mammals?
4. What happens with during cleavage?
5. What is gastrulation?
6. What is organogenesis?
7. What are the 4 extra-embryonic membranes in the amniotic egg?
8. How does mammalian development occur?
9. What three things influence cell fate?
10. How are organisms formed from the fertilized egg?
11. Can cells de-differentiate?
12. How was Dolly cloned?
- Nuclear transplantation
Fig. 21.7 Reproductive Cloning of a Mammal by Nuclear Transplantation
APPLICATION This method is used to produce cloned
animals whose nuclear genes are identical to the donor
animal supplying the nucleus.
1
RESULTS
The cloned animal is identical in appearance
and genetic makeup to the donor animal supplying the nucleus,
but differs from the egg cell donor and surrogate mother.
2
Egg cell
from ovary Nucleus
Nucleus
removed
3 Cells fused
removed
TECHNIQUE
Shown here is the procedure used to produce
Dolly, the first reported case of a mammal cloned using the nucleus
of a differentiated cell.
Egg cell
donor
Mammary
cell donor
Cultured
mammary cells
are semistarved,
arresting the cell
cycle and causing
dedifferentiation
Nucleus from
mammary cell
4 Grown in culture
Early embryo
5 Implanted in uterus
of a third sheep
6 Embryonic
development
Surrogate
mother
Lamb (“Dolly”)
genetically identical to
mammary cell donor
Figure 21.9 Working with stem cells
Embryonic stem cells
Adult stem cells
Early human embryo
at blastocyst stage
(mammalian equivalent of blastula)
From bone marrow
in this example
Totipotent
cells
Pluripotent
cells
Cultured
stem cells
Different
culture
conditions
Different
types of
differentiated
cells
Liver cells
Nerve cells
Blood cells
Chapter 47: Animal Development
1. What exactly happens when sperm meets egg?
2. What happens with activation of the egg?
3. What happens in mammals?
4. What happens with during cleavage?
5. What is gastrulation?
6. What is organogenesis?
7. What are the 4 extra-embryonic membranes in the amniotic egg?
8. How does mammalian development occur?
9. What three things influence cell fate?
10. How are organisms formed from the fertilized egg?
11. Can cells de-differentiate?
12. How was Dolly cloned?
13. When is a cell determined (fated)?
- Muscle cells – MyoD transcription factor – turns on all muscle genes
Figure 21.10 Determination and differentiation of muscle cells
Nucleus
Master control gene myoD
Other muscle-specific genes
DNA
Embryonic
precursor cell
OFF
OFF
Figure 21.10 Determination and differentiation of muscle cells
Nucleus
Master control gene myoD
Other muscle-specific genes
DNA
OFF
Embryonic
precursor cell
1
Myoblast
(determined)
Determination. Signals from other
cells lead to activation of a master
regulatory gene called myoD, and
the cell makes MyoD protein, a
transcription factor. The cell, now
called a myoblast, is irreversibly
committed to becoming a skeletal
muscle cell.
OFF
OFF
mRNA
MyoD protein
(transcription
factor)
Figure 21.10 Determination and differentiation of muscle cells
Nucleus
Master control gene myoD
Other muscle-specific genes
DNA
OFF
Embryonic
precursor cell
1
Myoblast
(determined)
2
Determination. Signals from other
cells lead to activation of a master
regulatory gene called myoD, and
the cell makes MyoD protein, a
transcription factor. The cell, now
called a myoblast, is irreversibly
committed to becoming a skeletal
muscle cell.
Differentiation. MyoD protein stimulates
the myoD gene further, and activates
genes encoding other muscle-specific
transcription factors, which in turn
activate genes for muscle proteins. MyoD
also turns on genes that block the cell
cycle, thus stopping cell division. The
nondividing myoblasts fuse to become
mature multinucleate muscle cells, also
called muscle fibers.
OFF
OFF
mRNA
MyoD protein
(transcription
factor)
mRNA
MyoD
Muscle cell
(fully differentiated)
mRNA
Another
transcription
factor
mRNA
mRNA
Myosin, other
muscle proteins,
and cell-cycle
blocking proteins
Chapter 47: Animal Development
1. What exactly happens when sperm meets egg?
2. What happens with activation of the egg?
3. What happens in mammals?
4. What happens with during cleavage?
5. What is gastrulation?
6. What is organogenesis?
7. What are the 4 extra-embryonic membranes in the amniotic egg?
8. How does mammalian development occur?
9. What three things influence cell fate?
10. How are organisms formed from the fertilized egg?
11. Can cells de-differentiate?
12. How was Dolly cloned?
13. When is a cell determined (fated)?
14. What is apoptosis?
- Programmed cell death – cell suicide
Figure 21.18 Molecular basis of apoptosis in C. elegans
Ced-9
protein (active)
inhibits Ced-4
activity
Death
signal
receptor
Mitochondrion
Ced-4 Ced-3
Inactive proteins
Cell
forms
blebs
(a) No death signal
Ced-9
(inactive)
Death
signal
Active Active
Ced-4 Ced-3
Activation
cascade
(b) Death signal
Other
proteases
Nucleases
Chapter 47: Animal Development
1. What exactly happens when sperm meets egg?
2. What happens with activation of the egg?
3. What happens in mammals?
4. What happens with during cleavage?
5. What is gastrulation?
6. What is organogenesis?
7. What are the 4 extra-embryonic membranes in the amniotic egg?
8. How does mammalian development occur?
9. What three things influence cell fate?
10. How are organisms formed from the fertilized egg?
11. Can cells de-differentiate?
12. How was Dolly cloned?
13. When is a cell determined (fated)?
14. What is apoptosis?
15. What are some model organisms for studying development?
Figure 21.2 Model Organisms for Genetic Studies of Development
DROSOPHILA MELANOGASTER
(FRUIT FLY)
Drosophila
- small, easy & cheap to culture
- 2 week generation time
- 4 chromosomes
- LARGE literature of info
CAENORHABDITIS ELEGANS
(NEMATODE)
C elegans
- easy to culture
- transparent body with few cell types
- zygote to mature adult in 3 days
0.25 mm
ARABIDOPSIS THAMANA
(COMMON WALL CRESS)
MUS MUSCULUS
(MOUSE)
Mouse
- vertebrate
- LARGE literature
- transgenics & knock-outs
DANIO RERIO
(ZEBRAFISH)