That the zona-binding represents a decisive step in the fertilization cascade can perhaps be seen in the fact that the zona-binding is species specific; the subsequent binding of the oocyte membrane onto the oolemma, on the other hand, is not.
When the acrosome reaction has been completed, the spermatozoon is now covered at its upper end only by the former inner membrane of the acrosome. For the further progress of the fertilization this is decisive because structures are thereby uncovered which are necessary for contact with the oocyte. One consequence of this is that changes appear, especially in the post-acrosomal membrane area of the spermatozoon.
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