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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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Table 27.12
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The tissues and organs of a tadpole emerge
from cells of the ectoderm, mesoderm, and
endoderm
Figure 27.12D
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
– programmed
cell death
(apoptosis)
Cell
suicide
Dead cell
engulfed and
digested by
adjacent
cell
Figure 27.13B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• 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