Question

What are the two main safeguards protecting eggs against polyspermy?

Answer 1

Polyspermy: The process of fertilization of eggs by more than one sperm is called polyspermy.

Two primary safeguards for protection against polyspermy:

1. Polyspermy at the plasma membrane level is prevented wherein the union of the first sperm leads to depolarization of the membrane and sheds the sperm receptors of the egg – Folr4 hence it checks the union of other sperms
2. Fertilization stimulates exocytosis of cortical granules – cortical reaction. These granules comprise enzymes that alter and hence stiffen the zona pellucida. This reduces the binding affinity of the sperm by the cleavage of the zona pellucida protein ZP2 causing the zona to be impermeable to other sperms