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2011_Questions_Week_2_Answers (1)

2011_Questions_Week_2_Answers (1) - Questions 1 The table...

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Questions: 1. The table below indicates the S-phase and M-phase for zygotes immediately upon fertilization and in the next two complete cell cycles are listed. Indicate the presence (+) or absence (-) of each of the component during each stage. *This is actually a bit of simplification. All Cyclin B is destroyed at the end of M-phase, and then gradually builds up during S-phase. **Immediatley at fertilization, cyclin B protein levels are very low but are quickly translated and cyclin B protein starts to build up. (see bottom p. 143 and top p.145 of book). In this sense, this first S-phase is not so very different than the others. 2. You treat Xenopus oocytes with A23817, a calcium ionophore. What will be the first major visual change in the eggs? It will cause the cortical granule reaction (visible fertilization envelope) 3. You assay primary oocytes that are still in their primary cell cycle arrest. How many chromosomes are present at this stage? The are 4 copies of each chromosome. 4. What causes the vitelline envelope to swell after the cortical granule reaction?
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