What is the role of the zona pellucida during fertilization?

The zona pellucida is a glycoprotein-rich extracellular matrix surrounding the oocyte (egg) that plays a critical role during fertilization. One of its primary functions is to prevent polyspermy, which is the occurrence of multiple sperm fertilizing the egg. This is achieved through a process called the fast block to polyspermy, where changes in the electrical potential of the egg membrane occur almost immediately after the first sperm binds to it. Additionally, once fertilization occurs, the zona pellucida undergoes biochemical changes that effectively block any additional sperm from attaching and entering the egg.

This mechanism is vital for ensuring that the resulting zygote has the correct amount of genetic material, as sperm contribute half of the genetic information while the egg contributes the other half. If multiple sperm were to enter, it could lead to an abnormal number of chromosomes and result in developmental issues for the embryo.

The other choices, while related to aspects of fertilization and early development, do not accurately describe the primary role of the zona pellucida. It does not nourish the developing embryo directly, facilitate sperm entry, or store genetic information. Rather, its focus is on providing a barrier and signaling framework for successful fertilization.