Question

What Prevents More Than One Sperm from Entering the Egg?

Answer 1

Fertilization:

1. The cortical reaction is a process initiated during fertilization that prevents polyspermy, the fusion of multiple sperm with one egg.
2. In order to refrain from the event of multi-sperm fertilization, the moment sperm penetrate into the zona pellucida successfully, this region experiences a sequence of biochemical changes that freezes the further sperm cells at various phases of penetration thus avoiding any more advancements.
3. This phenomenon is known as the zona reaction and the efficiency of the zona reaction decreases in the aging oocyte.
4. A chain of changes in the vitelline membrane is the second mechanism of protection by the oocyte occurring after it unites with one sperm, this is known as the vitelline reaction.
5. Both these processes form a generic defense mechanism known as a cortical reaction.