Biology, Seventh Edition
Solomon • Berg • Martin
Chapter 49
Animal Development
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Biology, Seventh Edition
CHAPTER 49 Animal Development
• Four processes of fertilization
• Contact and recognition between
noncellular egg coverings and
sperm
• Sperm entry is regulated
• Fertilization actives the egg
• Sperm and egg pronuclei fuse and
initiate DNA synthesis
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Biology, Seventh Edition
CHAPTER 49 Animal Development
• Fertilization in echinoderms
• Coverings of echinoderm eggs
–Vitelline envelope and jelly coat
• Sperm undergoes an acrosome
reaction, which facilitates penetration of
the egg coverings
• Followed by a fast block to polyspermy
and a slow block to polyspermy
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Biology, Seventh Edition
CHAPTER 49 Animal Development
Fertilization
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Biology, Seventh Edition
CHAPTER 49 Animal Development
The cortical
reaction
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Biology, Seventh Edition
CHAPTER 49 Animal Development
• Early development of the fetus
• The zygote undergoes cleavage
–Rapid cell divisions with a growth
phase
–Partitions the zygote into blastomeres
• Cleavage forms the morula and
then usually the blastula
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Biology, Seventh Edition
CHAPTER 49 Animal Development
Cleavage and gastrulation in amphioxus
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Biology, Seventh Edition
CHAPTER 49 Animal Development
Spiral cleavage in an annelid embryo
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Biology, Seventh Edition
CHAPTER 49 Animal Development
Cleavage pattern in a frog egg
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Biology, Seventh Edition
CHAPTER 49 Animal Development
Cleavage in a bird embryo
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Biology, Seventh Edition
CHAPTER 49 Animal Development
Cytoplasmic
determinants
in frog
development
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Biology, Seventh Edition
CHAPTER 49 Animal Development
• Gastrulation
• Process by which the blastula
becomes a three-layered embryo
or gastrula
–Zygote
–Early cleavage stages
–Morula
–Blastula
–Gastrula
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Biology, Seventh Edition
CHAPTER 49 Animal Development
Gastrulation in a frog embryo
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Biology, Seventh Edition
CHAPTER 49 Animal Development
Gastrulation in birds
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Biology, Seventh Edition
CHAPTER 49 Animal Development
• Organogenesis
• Gastrulation leads to
organogenesis, or organ formation
• Cells of the three germ layers
–Continue the processes of pattern
formation
–Leads to the formation of specific
structures
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Biology, Seventh Edition
CHAPTER 49 Animal Development
Fate of the germ layers formed at gastrulation
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Biology, Seventh Edition
CHAPTER 49 Animal Development
Development
of the human
nervous
system
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Biology, Seventh Edition
CHAPTER 49 Animal Development
Formation of the heart in birds and mammals
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Biology, Seventh Edition
CHAPTER 49 Animal Development
• In terrestrial vertebrates, the
three germ layers give rise to four
extraembryonic membranes
• Chorion used in gas exchange
• Amnion, a fluid-filled sac
• Allantois, which stores wastes
• Yolk sac, which makes food
available to the embryo
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Biology, Seventh Edition
CHAPTER 49 Animal Development
Extraembryonic membranes
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Biology, Seventh Edition
CHAPTER 49 Animal Development
• Early human development
• Fertilization occurs in the oviduct
• Cleavage takes place as the
embryo moves down the oviduct
toward the uterus
• The blastocyst undergoes
implantation in the endometrium
• The umbilical cord connects the
embryo to the placenta
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Biology, Seventh Edition
CHAPTER 49 Animal Development
Implantation
and early
development
in the uterus
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Biology, Seventh Edition
CHAPTER 49 Animal Development
• Prenatal and postnatal life
• Human prenatal development
requires 266 days
–Organogenesis begins during the first
trimester and continues throughout
–After the first two months, the embryo
is referred to as a fetus
–The neonate undergoes rapid
adaptations, especially in the
respiratory and digestive systems
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Biology, Seventh Edition
CHAPTER 49 Animal Development
Developmental
events in the
human embryo
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Biology, Seventh Edition
CHAPTER 49 Animal Development
The second
month of
development
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Biology, Seventh Edition
CHAPTER 49 Animal Development
Human fetus
at ten weeks
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Biology, Seventh Edition
CHAPTER 49 Animal Development
• Aging
• Marked by a decrease in
homeostatic response to stress
• All body systems decline with age,
but not at the same rate
–Examples include loss of taste buds
and axons in spinal nerves
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