© 1997 Chris Patton, Stanford University
Sperm undergoes the acrosome reaction and binds with the egg. Fusion occurs, actin polymerizes in the egg, the cortical granules fuse with plasma membrane and release their contents. This causes the fertilization membrane to rise. The sperm is pulled into the egg with help from the fertilization cone. Microtubules started at the male centrosome help push the sperm to the center of the egg to fuse with the female pro-nucleus.