After fertilization, all embryos undergo cleavage. In the Xenopus embryo, what is the relationship of the...

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Biology

After fertilization, all embryos undergo cleavage. In theXenopus embryo, what is the relationship of the animal-vegetal axisto the plane of the first three cleavages? Describe how cleavage inthe chick embryo differs from cleavage in frogs and mice; why dothese differences occur?

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After fertilization Xenopus embryos undergo cell cycles that have characteristic features During the first 90minute cell cycle cortical cytoplasmic movements and male and female pronuclear fusion occur The next eleven divisions occur at 20 to 30minute intervals with no gap phases while the embryo forms a ball of 4000 cells which encloses a fluidfilled blastocoel cavity This midblastula embryo has three regions the animal cap which forms the roof of the blastocoel the equatorial or marginal zone the walls of the blastocoel and the vegetal mass the blastocoel floor Although all midblastula cells are pluripotent Heasman et al 1984 explants of the animal cap form ectodermal derivatives in culture while equatorial explants form mesoderm and vegetal explants form endoderm At the end of the twelfth cycle gap phases reappear the cell cycle lengthens to 50 minutes and zygotic transcription starts this is called the See Answer

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