BIOL303 Lecture Notes - Lecture 6: Maternal Effect, Primitive Streak, Polyspermy
5 Dec 2016
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Document Summary
Drosophila egg activation: occurs as eggs pass through the oviduct, pressure triggers release of calcium: completion of meiosis 2. Micropyle: region on the vitelline envelope that allows entry on single sperm - eventually becomes anterior dorsal region. Polyspermy block: sperm are large and only one can enter the egg (no cortical granule reaction needed to block polyspermy) Syncytium: rapid super cial cleavage where many nuclei share a common cytoplasm. Pole cells: after 9th division, pole cells autonomously specify and migrate outside of the syncytium. Syncytial blastoderm: nuclei have migrated to cortex and undergone 3 more cortical synchronous divisions. Cellular blastoderm: increase in transcription of zygotic genes result in cellularization and asynchronous divisions after 13th. Mid blastula transition: slowing of nuclear divisions, onset of cellularization, and increase in zygotic mrna transcription. Dna to cytoplasmic ratio: increasing the amount of dna without increasing the cytoplasmic volume dilutes repressors.
