1!Biology 624 - Developmental Genetics!Lecture #4 - Cleavage !Outcomes of CLEAVAGE CYCLES-!1. Rapid increase in cell number!2. Distribution of egg contents, often !asymmetrically, to the cells !Cell Cycle of Somatic Cells!Cell Cycle of Early Blastomeres!Cleavage patterns affected by--!--the amount and location of yolk!--how complete cleavage (cytokinesis) is!--relationship of cleavage planes !--timing of cleavage divisions relative to !each other!C. Elegans Lineage Diagram!2!Worm cleavage --!--point of sperm entry is posterior pole!--sperm centriole organizes microtubules !to ferry determinants to front or back!--cytoplasmic “streams” also move! molecules around! PAR proteins during cleavage in C. elegans!PAR-3 = orange"PAR-2 = purple" Cleavage in Caenorhabditis elegans!Skn-1 is required to specify pharynx and gut of C. elegans!Cell-Cell Interactions Are Required for the"EMS Cell to Form Intestinal Lineage Determinants!Cell-Cell Signaling in the 4-Cell Embryo of C. elegans!3!Development of a Human Embryo From Fertilization to Implantation!Early Cleavage in Mammals!SEMs of (A) Uncompacted and (B) Compacted 8-cell Mouse Embryos!The Cleavage of a Single Mouse Embryo In Vitro!Hallmarks of the Mid-Blastula Transition:!--N/C ratio approaches 1!--cell cycle lengthens and incorporates G1, G2!--transcription from embryo nuclei activated!--cells become
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