Final answer:
Gametic incompatibility is the method of protecting genetic isolation of a population by preventing the fertilization of eggs of a different species.
Step-by-step explanation:
The method of protecting the genetic isolation of a population that involves the inability of sperm to fertilize eggs of a different species is called gametic incompatibility. This is a type of prezygotic barrier that prevents reproduction from taking place. It occurs when there are differences in the gamete cells (eggs and sperm) of different species, which results in the inability of the sperm to fertilize the eggs of a different species.