Develop. Bio. - Cleavage Cleavage- a series of mitotic...

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Cleavage Cleavage - a series of mitotic divisions whereby the enormous volume of egg cytoplasm is divided into numerous smaller nucleated cells, involves karyokinesis and cytokinesis. Blastomeres - cleavage-stage cells. Karyokinesis - mitotic division of the nucleus, movement of the chromosomes, mechanical agent is mitotic spindle which is composed of microtubules made of tubulin. Cytokinesis - The division of the cell, mechanical agent is contractile ring of microfilaments made of actin. Cleavage furrow - is created by the contractile ring that eventually bisects the plane of mitosis, creating two genetically equivalent blastomeres. Meroblastic - only a portion of the cytoplasm is cleaved. Holoblastic - cleavage furrow is extended through the whole cytoplasm. (complete) Type of Cleavage Group of Animals (Species) 1. Radial Holoblastic Sea cucumber, Sea Urchin, Frog 2. Spiral Holoblastic Molluscs 3. Bilateral Holoblastic Turnicate, Stylela (pre- vertebrate) 4. Rotational Holoblastic Mammals 5. Discoidal Meroblastic Birds and Fish 6. Superficial Meroblastic Fly Isolecithal - sparse, equally spaced yolk. (ex: sea urchins, mammals) Telolecithal - dense yolk concentrated in one end of the egg (ex: birds and fishes) Centrolecithal - the yolk is concentrated in the center. (ex: insects) Mesolecithal - moderately telolecithal Gastrulation Gastrulation - is the process of highly coordinated cell and tissue movements whereby the cells of the blastula are dramatically rearranged.
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Invagination - the folding of a region of cells, much like the indenting of a soft rubber ball when it is poked. Ex: sea urchin endoderm Involution - the inturning or inward movement of an expanding outer layer so that it spreads over the internal surface of the remaining external cells. Ex: Amphibian mesoderm Ingression- the migration of individual cells from the surface layer into the interior of the embryo. Ex: Sea urchin mesoderm, Drosophila nueroblasts. Delamination
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This note was uploaded on 04/16/2008 for the course DEVELOPMEN 3302 taught by Professor Held during the Spring '08 term at Texas Tech.

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Develop. Bio. - Cleavage Cleavage- a series of mitotic...

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