ANIMAL BLOCK OF POLYSPERMY. “In animals like frogs and several marine invertebrates, polyspermy (the fertilization of an egg by two or more sperm cells) is prevented by an electrical charge across the surface of the egg (fast block in a few seconds) and/or by modification of the extracellular egg coat by a secretion reaction (slow block in dozens of seconds), following gamete fusion. A Ca2+ wave in the fertilized egg triggers the secretion reaction associated with the slow polyspermy block.”
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