Chapter 43: Animal Development
CHAPTER 43
Animal Development
Chapter 43: Animal Development
Chapter 43: Animal
Development
Fertilization: Interactions of Sperm and Egg
Cleavage: Repackaging the Cytoplasm
Gastrulation: Producing the Body Plan
Chapter 43: Animal Development
Chapter 43: Animal
Development
Neurulation: Initiating the Nervous System
Extraembryonic Membranes
Human Pregnancy and Birth
Chapter 43: Animal Development
Fertilization: Interactions of
Sperm and Egg
•
•
•
•
Fertilization involves sperm activation
the acrosomal reaction
digestion of a path thru outer egg covering
species-specific binding of sperm to outer
egg covering
• fusion of sperm and egg cell membranes.
Review Figure 43.1
4
Chapter 43: Animal Development
figure 43-01.jpg
Figure
43.1
Figure 43.1
Chapter 43: Animal Development
Fertilization: Interactions of
Sperm and Egg
• Entry of sperm into egg triggers fast and
slow blocks to polyspermy, and in mammals,
signals the egg to complete meiosis and
begin development.
Review Figures 43.2, 43.3, 43.4
6
Chapter 43: Animal Development
figure 43-02.jpg
Figure
43.2
Figure 43.2
Chapter 43: Animal Development
figure 43-03.jpg
Figure
43.3
Figure 43.3
Chapter 43: Animal Development
figure 43-04.jpg
Figure 43.4
Figure 43.4
Chapter 43: Animal Development
Fertilization: Interactions of
Sperm and Egg
• Sperm and egg contribute differentially to
the zygote.
• The sperm contributes a haploid nucleus
and, in some species, a centriole.
• The egg contributes a haploid nucleus,
nutrients, ribosomes, mitochondria, and
informational molecules that will control
early stages of development.
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Chapter 43: Animal Development
Fertilization: Interactions of
Sperm and Egg
• The cytoplasmic contents of the egg are not
distributed homogeneously, and are
rearranged after fertilization to set up the
major axes of the future embryo.
Review Figures 43.5, 43.6
11
Chapter 43: Animal Development
figure 43-05.jpg
Figure
43.5
Figure 43.5
Chapter 43: Animal Development
figure 43-06a.jpg
Figure 43.6
– Part 1
Figure 43.6 – Part 1
Chapter 43: Animal Development
Figure 43.6
– Part 2
Figure 43.6 – Part 2
figure 43-06b.jpg
Chapter 43: Animal Development
Cleavage: Repackaging the
Cytoplasm
• In most animals, cleavage is a period of
rapid cell division without cell growth or
gene expression.
• During cleavage, the cytoplasm of the
zygote is repackaged into smaller and
smaller cells.
15
Chapter 43: Animal Development
Cleavage: Repackaging the
Cytoplasm
• Cleavage pattern is influenced by amount of
yolk impeding cleavage furrow formation
and orientation of mitotic spindles.
• The result of cleavage is a mass of cells
called a blastula.
Review Figure 43.7
16
Chapter 43: Animal Development
figure 43-07a.jpg
Figure 43.7
– Part 1
Figure 43.7 – Part 1
Chapter 43: Animal Development
figure 43-07b.jpg
Figure 43.7
– Part 2
Figure 43.7 – Part 2
Chapter 43: Animal Development
Cleavage: Repackaging the
Cytoplasm
• Cleavage in mammals is unique in that cell
divisions are much slower and genes are
expressed early in the process.
• Cleavage results in an inner cell mass that
becomes the embryo and an outer cell mass
that becomes the trophoblast.
• The mammalian embryo at this stage is
called a blastocyst.
Review Figure 43.8
19
Chapter 43: Animal Development
figure 43-08.jpg
Figure
43.8
Figure 43.8
Chapter 43: Animal Development
Cleavage: Repackaging the
Cytoplasm
• Fate maps, which identify what tissues and
organs will form from particular
blastomeres, can be created for the
blastula.
Review Figure 43.9
21
Chapter 43: Animal Development
figure 43-09.jpg
Figure
43.9
Figure 43.9
Chapter 43: Animal Development
Cleavage: Repackaging the
Cytoplasm
• Some species undergo mosaic development:
the fate of each cell is determined by the 8cell stage.
• Other species undergo regulative
development: cells are not determined so
early and can change developmental fates.
• In these species, blastomeres separated at
early stages can develop into complete
embryos, which are then monozygotic, or
identical, twins. Review Figure 43.10
23
Chapter 43: Animal Development
figure 43-10a.jpg
Figure 43.10 –
Part 1
Figure 43.10 – Part 1
Chapter 43: Animal Development
figure 43-10b.jpg
Figure 43.10
– Part 2
Figure 43.10 – Part 2
Chapter 43: Animal Development
Gastrulation: Producing the
Body Plan
• Gastrulation involves massive cell
movements that produce three primary
germ layers and place cells from various
regions of the blastula into new associations
with one another.
Review Table 43.1
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Chapter 43: Animal Development
table 43-01.jpg
Table
43.1
Table 43.1
Chapter 43: Animal Development
Gastrulation: Producing the
Body Plan
• The initial step of sea urchin and amphibian
gastrulation is inward movement of certain
blastomeres.
• The site of inward movement becomes the
blastopore.
• Cells that move into the blastula become the
endoderm and mesoderm; cells remaining on the
outside become the ectoderm.
• Cytoplasmic factors in the vegetal pole cells are
essential to initiate development.
Review Figure 43.11, 43.12
28
Chapter 43: Animal Development
figure 43-11.jpg
Figure
43.11
Figure 43.11
Chapter 43: Animal Development
figure 43-12.jpg
Figure 43.12
Figure 43.12
Chapter 43: Animal Development
Gastrulation: Producing the
Body Plan
• Gastrulation in frogs is initiated when cells
in the gray crescent move into the
blastocoel.
• This inward migration creates the
blastopore.
• The dorsal lip of the blastopore is a critical
site for the determination of tissues.
• It has been called the primary embryonic
organizer.
Review Figures 43.13, 43.14, 43.15
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Chapter 43: Animal Development
figure 43-13a.jpg
Figure
43.13 –
Part 1
Figure 43.13 – Part 1
Chapter 43: Animal Development
Figure 43.13
– Part 2
Figure 43.13 – Part 2
figure 43-13b.jpg
Chapter 43: Animal Development
figure 43-14.jpg
Figure 43.14
Figure 43.14
Chapter 43: Animal Development
Figure 43.15 –
Part 1
Figure 43.15 – Part 1
figure 43-15a.jpg
Chapter 43: Animal Development
figure 43-15b.jpg
Figure
43.15 –
Part 2
Figure 43.15 – Part 2
Chapter 43: Animal Development
Gastrulation: Producing the
Body Plan
• The anterior–posterior axis of the frog
blastula appears to be determined by the
distribution of the protein -catenin
• This activates a signaling cascade that
induces the primary embryonic organizer.
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Chapter 43: Animal Development
Gastrulation: Producing the
Body Plan
• Gastrulation in reptiles and birds differs
from that in sea urchins and frogs because
the large egg yolk causes the blastula to
form a flattened disc of cells.
Review Figure 43.16
38
Chapter 43: Animal Development
figure 43-16a.jpg
Figure
43.16 –
Part 1
Figure 43.16 – Part 1
Chapter 43: Animal Development
figure 43-16b.jpg
Figure
43.16 –
Part 2
Figure 43.16 – Part 2
Chapter 43: Animal Development
Gastrulation: Producing the
Body Plan
• Mammals have a pattern of gastrulation
similar to that of birds, even though they
have no yolk.
Review Figure 43.17
41
Chapter 43: Animal Development
figure 43-17.jpg
Figure
43.17
Figure 43.17
Chapter 43: Animal Development
Neurulation: Initiating the
Nervous System
• Neurulation follows gastrulation.
• Cells that migrate over the dorsal lip of the
blastopore are determined to be chordomesoderm,
which forms the notochord.
• The notochord induces the overlying ectoderm to
thicken, form parallel ridges, and fold in on itself to
form a neural tube below the epidermal ectoderm.
• The nervous system develops from the neural tube.
Review Figure 43.18
43
Chapter 43: Animal Development
Figure 43.18
– Part 1
Figure 43.18 – Part 1
figure 43-18a.jpg
Chapter 43: Animal Development
figure 43-18b.jpg
Figure 43.18
– Part 2
Figure 43.18 – Part 2
Chapter 43: Animal Development
figure 43-18c.jpg
Figure 43.18
– Part 3
Figure 43.18 – Part 3
Chapter 43: Animal Development
Neurulation: Initiating the
Nervous System
• The notochord and neural crest cells
participate in the segmental organization of
tissues called somites along the body axis.
• Rudimentary organs and organ systems
form during this stage.
Review Figure 43.19
47
Chapter 43: Animal Development
figure 43-19.jpg
Figure 43.19
Figure 43.19
Chapter 43: Animal Development
Neurulation: Initiating the
Nervous System
• Four families of Hox genes determine
anterior–posterior pattern differentiation
along the body axis in mammals.
• Other genes such as sonic hedgehog,
contribute to dorsal–ventral differentiation.
Review Figure 43.20
49
Chapter 43: Animal Development
figure 43-20a.jpg
Figure 43.20
– Part 1
Figure 43.20 – Part 1
Chapter 43: Animal Development
Figure 43.20
– Part 2
Figure 43.20 – Part 2
figure 43-20b.jpg
Chapter 43: Animal Development
Extraembryonic Membranes
• The embryos of reptiles, birds, and mammals are
protected and nurtured by four extraembryonic
membranes.
• In birds and reptiles the yolk sac surrounding the
yolk provides nutrients to the embryo
• The chorion lines the eggshell and participates in
gas exchange
• The amnion surrounds the embryo enclosing it in
an aqueous environment
• The allantois stores metabolic wastes.
Review Figure 43.21
52
Chapter 43: Animal Development
figure 43-21.jpg
Figure
43.21
Figure 43.21
Chapter 43: Animal Development
Extraembryonic Membranes
• In mammals, the chorion and the
trophoblast cells interact with the maternal
uterus to form a placenta, for nutrient and
gas exchange.
• The amnion encloses the embryo in an
aqueous environment.
Review Figure 43.22
54
Chapter 43: Animal Development
figure 43-22.jpg
Figure
43.22
Figure 43.22
Chapter 43: Animal Development
Extraembryonic Membranes
• Samples of amniotic fluid or pieces of
chorion can be taken during pregnancy and
analyzed for evidence of genetic disease.
Review Figure 43.23
56
Chapter 43: Animal Development
figure 43-23.jpg
Figure
43.23
Figure 43.23
Chapter 43: Animal Development
Human Pregnancy and Birth
• Pregnancy in humans can be divided into
three trimesters.
• Early embryogenesis occurs in the first
trimester; during this time, the embryo is
vulnerable to damage that could lead to
birth defects.
• Hormonal changes, including high hCG,
estrogen, and progesterone levels, block
further ovulation and menstruation and
cause symptoms of pregnancy.
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Chapter 43: Animal Development
Human Pregnancy and Birth
• During the second and third trimesters the
embryo grows, the limbs elongate, and
organ systems mature.
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Chapter 43: Animal Development
Human Pregnancy and Birth
• The onset of labor is due to many hormonal
and mechanical factors, which increase
contractility of uterine muscles. Oxytocin
plays a major role in a positive feedback
loop.
Review Figure 43.25
60
Chapter 43: Animal Development
figure 43-25.jpg
Figure
43.25
Figure 43.25
Chapter 43: Animal Development
Human Pregnancy and Birth
• Birth is not the end of development, which
continues throughout childhood and
throughout life.
62