BIO 121 Lecture Notes - Lecture 29: Symmetry In Biology, Polarity In Embryogenesis, Centriole
24 Jul 2020
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Document Summary
Cytoplasmic factors in oocyte set up signalling cascades that regulate major events. Beta-catenin = key transcription factor found through cytoplasm. Gsk 3 (a molec) found thruout cytoplasm targets beta-catenin for degradation (keeps b-c under control: in vegetal hemisphere there is a protein that inhibits gsk 3. Sperm enters passes on centrioles microtubules change rotation of cytoplasm vesicles move & move to side opps sperm entry become active. Protein that inhibits gsk 3 is activated beta-catenin not degraded increase in transcription factors on dorsal region. Create dorsal-ventral axis & gradient of transcription factors continues as embryo develops. Complete cleavage occ in eggs /w little yolk: those /w more yolk division unequal & daughter cells in animal pole are smaller. Incomplete cleavage occ in eggs /w lots of yolk cleavage furrows don"t penetrate: discoidal cleavage embryo forms as blastodisc that sits on top of yolk. Superficial cleavage variation of incomplete cleavage in insects. 1st division parallel to animal-vegetal axis gives 2 blastomeres.
