HELP: regulative embryos, nuclear equivelance..,

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      I’m taking embryology right now, and it’s lecture based (ie. no textbook), and I cant find anything on google.

      Anyway, in class we covered regulative embryos.

      —the diagram Im looking at has a labeled animal pole that says "has nucleus" and a labeled vegetal pole that says "has yolk + food". Does that mean that the nucleus is ONLY found in the Animal pole?


      we talked about several experiments related to regulative embryos, 2 of which I don’t understand.

      1) Frog egg Fusion experiment. If the eggs are fused in the wrong orientation (egg #1 with animal pole on top and vegetal pole at bottom. egg #2: the opposite), a larva does not form. My question is, why is that?

      2) Cutting experiment. When a horizental cut is done to the second cell stage, 4 cells form (2 balls of celiated cells, and 2 cells that can’t form a complete embryo).
      However, regularly the cell devides horizentally at the 4 cells stage. When 8 cells form, non of them can for a complete embryo on their own.
      my quesion is that, what’s the difference between these 2 cuts if we are going to end up with cells that can’t form a complete embryo on their own in both situations.
      I don’t really understand this cutting experiment too well. So a brief explaination would be helpful.

      and finally

      For testing nuclear equivelance, the experiment of "delayed nucleation causes twinning in a newt" says that when the string is tied, the side with the nucleus divides until the 16 cells stage, and then twinning occurs.
      From what I got, twinning is when the nucleus starts slipping into the cytoplasmic side, and starts dividing to reach the 16 cell stage. and that (having 2 sides, each with 16 cells) demonstrates nuclear equivelance. Is this the correct reasoning? and am i right about what twinning is?

      Any help would be great! thanks

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