What process prevents polyspermy during fertilization?

The process that prevents polyspermy during fertilization is the cortical reaction. This is a crucial mechanism that occurs shortly after a sperm cell successfully penetrates the oocyte (egg). The cortical reaction involves the release of calcium ions within the egg, which leads to changes in the egg's membrane and the formation of a fertilization membrane. This membrane acts as a barrier to additional sperm from binding to and entering the egg, thus ensuring that only one sperm can fertilize the egg and preventing the potentially detrimental effects of polyspermy, which can lead to abnormal development.

Gastrulation, cleavage, and blastulation are important stages in embryonic development but do not address the immediate prevention of polyspermy. Gastrulation is the phase where the embryo begins to form distinct layers, cleavage refers to the rapid cell divisions following fertilization, and blastulation involves the formation of a hollow ball of cells known as the blastula. Each of these processes occurs after fertilization has taken place and is not involved in the mechanisms that prevent multiple sperm from fertilizing the egg.