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BIOLOGY
CONCEPTS & CONNECTIONS
Fourth Edition
Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor
CHAPTER 27
Reproduction and Embryonic
Development
Modules 27.9 – 27.15
From PowerPoint® Lectures for Biology: Concepts & Connections
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
PRINCIPLES OF EMBRYONIC DEVELOPMENT
27.9 Fertilization results in a zygote and triggers
embryonic development
• The shape of a human sperm cell is adapted to
its function
Plasma membrane
Middle
piece
Neck
Head
Tail
Mitochondrion
(spiral shape)
Nucleus
Acrosome
Figure 27.9B
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• Only one of these
sperm will penetrate
this human egg cell
to initiate
fertilization
– Fertilization is the
union of a sperm
and an egg to form a
diploid zygote
Figure 27.9A
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• Process of
fertilization
1 The sperm
approaches
the egg
2 The sperm’s
acrosomal enzymes
digest the
egg’s jelly
3 Proteins on the
coat
sperm head bind
to egg receptors
SPERM
4 The plasma membranes
of sperm and egg fuse
Sperm
head
5 The sperm
nucleus
enters
the egg
cytoplasm
Nucleus
Acrosome
Acrosomal
Plasma
membrane enzymes
6 A
fertilization
envelope
forms
Receptor protein
molecules
Plasma
membrane
Jelly
coat
Vitelline
layer
Cytoplasm
EGG CELL
Sperm
nucleus
Egg
nucleus
7 The nuclei
of sperm
and egg fuse
Zygote
nucleus
Figure 27.9C
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27.10 Cleavage produces a ball of cells from the
zygote
• Cleavage is the first major phase of embryonic
development
– It is the rapid succession of cell divisions
– It creates a multicellular embryo from the zygote
– It partitions the multicellular embryo into
developmental regions
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Cleavage in
a sea urchin
ZYGOTE
2 cells
4 cells
8 cells
Blastocoel
Many cells
(solid ball)
Figure 27.10
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BLASTULA
(hollow ball)
Cross section
of blastula
27.11 Gastrulation produces a three-layered
embryo
• Gastrulation is the second major phase of
embryonic development
– It adds more cells to the embryo
– It sorts all cells into three distinct cell layers
– The embryo is transformed from the blastula
into the gastrula
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• The three layers produced in gastrulation
– Ectoderm, the outer layer
– Endoderm, an embryonic digestive tract
– Mesoderm, which partly fills the space between
the ectoderm and endoderm
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Animal pole
• Development of
frog gastrula
Blastocoel
1
Vegetal pole
BLASTULA
GASTRULATION
2
Blastopore
forming
Blastopore
forming
Blastocoel
shrinking
Archenteron
3
Archenteron
Ectoderm
Mesoderm
Endoderm
4
Yolk plug
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Yolk plug
GASTRULA
Figure 27.11C
27.12 Organs start to form after gastrulation
• Embryonic tissue layers begin to differentiate
into specific tissues and organ systems
• In chordates
– the notochord develops from the mesoderm
– the neural tube develops from the ectoderm
• The neural tube becomes the brain and spinal
cord
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Neural Neural
fold
plate
Neural
fold
Neural
plate
Notochord
Ectoderm
Mesoderm
Endoderm
Archenteron
Neural folds
Outer layer
of ectoderm
Neural tube
Figure 27.12A, B
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Neural tube
• Somites are
blocks of
mesoderm that
will give rise to
segmental
structures
• The body cavity,
or coelom, also
develops from
the mesoderm
Notochord
Somite
Coelom
Archenteron
(digestive cavity)
Somites
Tail bud
Eye
Figure 27.12C
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Table 27.12
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• The tissues and organs of a tadpole emerge
from cells of the ectoderm, mesoderm, and
endoderm
Figure 27.12D
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27.13 Changes in cell shape, cell migration, and
programmed cell death give form to the
developing animal
Ectoderm
• Tissues and organs
take shape in a
developing embryo
as a result of
– cell shape changes
– cell migration
Figure 27.13A
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– programmed
cell death
(apoptosis)
Cell
suicide
Dead cell
engulfed and
digested by
adjacent
cell
Figure 27.13B
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27.14 Embryonic induction initiates organ
formation
• Induction is the mechanism by which one group
of cells influences the development of tissues
and organs from ectoderm, endoderm, and
mesoderm
– Adjacent cells and cell layers use chemical
signals to influence differentiation
– Chemical signals turn on a set of genes whose
expression makes the receiving cells differentiate
into a specific tissue
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Induction during egg development
Lens ectoderm
Future
brain
Optic cup
Cornea
Lens
Optic
vesicle
Future
retina
Optic
stalk
1
2
3
4
Figure 27.14
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27.15 Pattern formation organizes the animal body
• Pattern formation is the emergence of a body
form with structures in their correct relative
positions
– It involves the response of genes to spatial
variations of chemicals in the embryo
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Wing development
ANTERIOR
Bird
embryo
VENTRAL
Normal wing
Limb bud
DISTAL
Limb bud develops
DORSAL
PROXIMAL
POSTERIOR
Figure 27.15A
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• Pattern-forming zone
Donor
limb
bud
Graft of cells
from patternforming
zone
Host
limb
bud
Wing with
duplication
Graft
Host limb bud develops
Donor cells
Host patternforming zone
Figure 27.15B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings