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Study Questions 1. If high-molecular-weight DNA, prepared by standard biochemical procedures, is injected into a frog egg, it may be assembled into chromatin or chromosome-like structures. Yet, if the same experiment is carried out by injecting DNA into somatic cells, the injected DNA does not assemble into chromatin. Can you explain the difference?
2. Three changes occur at the mid-blastula transition: transcription and motility increase, and the cell cycle lengthens. Perhaps all three events are regulated by some common "switch." Can you propose an experimental way to decide whether these events are linked in some regulatory scheme?
3. Predict what might occur if the animal cap of a living Xenopus blastula were microsurgically removed. Would gastrulation occur?
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