Molecular mechanisms of fertilization.

The fertilization process serves the species as a mechanism for increasing its genetic diversity and ultimately its evolutionary persistence. For the biologist, it provides many fundamental problems for study. Several different types of membrane fusion reactions occur, each with a specific role in the sequence of fertilization. The sperm faces problems in transport and interaction with the egg; the egg modifies its surface and its internal metabolism in response to fusion with the sperm; and all these processes contain a wealth of interesting biochemical and biophysical problems. Many systems under study are easily manipulated, and, as a result, different portions of the fertilization sequence can be studied in isolation. Despite the enormous progress and insights made on this problem over the last century, our understanding of fertilization is still tentative, and the above discussion should be viewed as a progress report. We are just beginning to obtain some of the clues to unravel the mechanism of the complex machinery that Aristotle predicted was in the egg.