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Vertebrate Development
Chapter 51
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Fertilization
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Penetration
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hydrolytic enzymes in acrosome of sperm head
Activation
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events initiated by sperm penetration
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egg nucleus complete second meiotic division

metabolic activity
Nuclei fusion Syngamy - fusion of sperm nucleus with egg nucleus to
form the diploid nucleus.
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Cell Cleavage Patterns
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Cleavage - size of cells
holoblastic cleavage Sea Urchins
meroblastic cleavage Reptiles and birds
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Cell Cleavage Patterns
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Mammals
– little yolk -holoblastic cleavage
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morula - Each cell is a blastomere.
blastula is formed
inner cell mass - embryo
trophoblast - implantation
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Blastula & Gastrulation
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Certain groups of cells invaginate and
involute from the surface of the blastula
during gastrulation.
– By the end of gastrulation - 3 germ layers
 ectoderm
 mesoderm
 endoderm
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Gastrulation in primitive chordates
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Gastrulation
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Gastrulation in most aquatic vertebrates
– Yolk-laden cells of the vegetal pole are fewer and much
larger than the yolk-free cells of the animal pole.
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Gastrulation
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Gastrulation in reptiles, birds, mammals
 primitive streak
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Extraembryonic Membranes
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Fluid-filled amniotic membrane an adaptation to terrestrial
life amnion, chorion, yolk sac, and allantois.
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Vertebrate Embryonic Development
Ontogeny recapitulates phylogeny
Embryological development (ontogeny) involves the same progression of
changes that have occurred during evolution (phylogeny
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