1. CHAPTER 27 Reproduction and Embryonic Development
Modules 27.9 – 27.15

2. The shape of a human sperm cell is adapted to its function
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
Middle piece
Neck
Head
Plasma membrane
Tail
Mitochondrion (spiral shape)
Nucleus
Acrosome
Figure 27.9B

3. 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

4. Process of fertilization1
The sperm approaches the egg 2
The sperm’s acrosomal enzymes digest the egg’s jelly coat 3
SPERM
Proteins on the sperm head bind to egg receptors 4
The plasma membranes of sperm and egg fuse
Sperm head 5
The sperm nucleus enters the egg cytoplasm
Nucleus
Acrosome
Acrosomal enzymes
Plasma membrane 6
A fertilization envelope forms
Receptor protein
molecules
Plasma membrane
Sperm nucleus
Vitelline layer
Cytoplasm
Egg nucleus
Jelly coat 7
The nuclei of sperm and egg fuse
EGG CELL
Zygote nucleus
Figure 27.9C

5. 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

6. BLASTULA (hollow ball) Cross section of blastula
Cleavage in a sea urchin
ZYGOTE
2 cells
4 cells
8 cells
Blastocoel
Many cells (solid ball)
BLASTULA (hollow ball)
Cross section of blastula
Figure 27.10

7. 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

8. 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

9. Development of frog gastrula
Animal pole
Blastocoel
Development of frog gastrula 1
Vegetal pole
BLASTULA
GASTRULATION 2
Blastopore forming
Blastopore forming
Blastocoel shrinking
Archenteron 3
Archenteron
Ectoderm
Mesoderm 4
Endoderm
Yolk plug
Yolk plug
GASTRULA
Figure 27.11C

10. 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

11. Neural plate
Neural fold
Neural fold
Neural plate
Notochord
Ectoderm
Mesoderm
Endoderm
Archenteron
Neural folds
Outer layer of ectoderm
Neural tube
Figure 27.12A, B

12. The body cavity, or coelom, also develops from the mesoderm
Neural tube
Somites are blocks of mesoderm that will give rise to segmental structures
Notochord
Somite
Coelom
Archenteron (digestive cavity)
The body cavity, or coelom, also develops from the mesoderm
Somites
Tail bud
Eye
Figure 27.12C

13. Table 27.12

14. The tissues and organs of a tadpole emerge from cells of the ectoderm, mesoderm, and endoderm
Figure 27.12D

15. Tissues and organs take shape in a developing embryo as a result of
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

16. programmed cell death (apoptosis)
Cell suicide
Dead cell engulfed and digested by adjacent cell
programmed cell death (apoptosis)
Figure 27.13B

17. 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

18. Induction during egg development
Optic cup
Lens ectoderm
Cornea
Future brain
Lens
Optic vesicle
Future retina
Optic stalk 1 2 3 4
Figure 27.14

19. 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

20. Wing development ANTERIOR Bird embryo VENTRAL Normal wing Limb bud
DISTAL
Limb bud develops
DORSAL
PROXIMAL
POSTERIOR
Figure 27.15A

21. Pattern-forming zone Graft of cells from pattern- forming zone
Wing with duplication
Graft
Donor limb bud
Host limb bud
Host limb bud develops
Host pattern- forming zone
Donor cells
Figure 27.15B