01:119:116 Lecture Notes - Lecture 16: Polarity In Embryogenesis, Meiosis, Blastula
1 Apr 2017
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Lecture 16 - development 1: introduction, development. Development = all changes that occur during a lifetime: model organisms. (where we left off in reproduction: sperm (usually flagellated and motile) fuses with ovum (larger and immotile) zygote (fertilized egg, single cell) What are the consequences of fertilization: restores diploid number, determines sex (sometimes, activates egg, reactions to start development. Steps in fertilization: acrosomal reaction, fast and/or slow block to polyspermy, cortical reaction, egg activation, karyogamy, first cleavage, sea urchin. Sperm contacts egg: sperm dissolves outer layer, molecules on sperm surface bind to egg (species specific, egg surface changes (polarizes) deters polyspermy. External fertilization - jelly coat chemicals attract sperm (chemotaxis) Protein molecules at tip bind to specific receptors. This happens in humans & sea urchins. Unfertilized egg cytoplasm negatively charged relative to outside. At fertilization ions channels in egg plasma membrane open na+ diffuse in and enters egg (the ocean is salty)
