Question

How is polyspermy blocked?

Answer 1

Polyspermy:

1. The process by which an oocyte is fertilized by more than one sperm is termed polyspermy.
2. Polyspermy leads to polyploidy which results in the formation of an abnormal embryo.

Blockage of polyspermy:

1. An ovum has several layers around it such as a vitelline membrane, corona radiata, and zona pellucida.
2. When the fertilization takes place sperm enters the membrane of the ovum certain chemical reactions take place that blocks the further entry of sperm.
3. The processes by which polyspermy is blocked are of two types:

• Fast block polyspermy: It takes place by changing the electric potential of the plasma membrane of the egg, the sperm depolarizes the egg membrane.
• Slow block polyspermy: Certain enzymes like hydrolases, peroxidase, etc. act on the zona pellucida layer and modify the ZP2 and ZP3 receptors on the zona pellucida layer making it harder.