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Fertilization is
Union between egg and sperm
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Fertilization does what 2 things?
- Recombination of genes and restores diploid status
- Also causes the start of cleavage
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What is a small ball of cells called (egg)?
Blastomeres
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Patterns of cleavage depends on?
- Quantity and type of yold present
- Type of symmetry inherited
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Isolethical yolk
- Very little yolk
- Evenly distributed in egg
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Holoblastic cleavage
- Cells are surrounded by a membrane.
- The cleavage furrow extends through the egg
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Telolecithal
- Telos=end
- Yolk is densly concentrated at the vegetal pole
- Disc shaped mass on top of yolk mass=vegetal pole
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Radial cleavage
- Pie-like characteristic of animals with backbones
- AKA-regulative
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Indeterminate
Cells of a blastomere are no identified as a specialty cell. If one cell is separated, it will form its own new blastomere.
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Symmetry of echinoderms and chordates
radial symmetry
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Spiral cleavage
Cleavage planes are oblique to the polar axis (animal/vegetal poles)
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Spiral cleavage
Platyhelminthes, molluscs
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Blastula
- Cluster of cells as a result of cleavage
- Outer layer becomes ectoderm
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Gastrulation
- Forms germ layers
- New cell association occurs to body plan (specialized)
- Invagination occurs-Deurterostomes, protostomes
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Ectoderm
Epithelium of body and nervous system
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Mensoderm
Muscles, reproductive, peritoneum
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Endoderm
Epithelial lining of digestive tract
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Echinodermata includes and means?
- External spines
- Starfish, sea cucumbers, sea lilies, sand dollars
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Charcteristic of echinoderms
- Spiny endoskeleton
- Water-vascular system
- Pericerllariae-Small pincers on the spine to remove debris
- Dermal branchiae or papulae
- Bilateral and pentaradial symmetry
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What is bilateral?
Larvae
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Habitat?
- Marine bottom dwellers
- Not found in fresh or brakish waters
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