Fusion protein could be targeted to stop parasites from reproducing. When two become one: the mysterious process of fertilisation.Getty Boy meets girl. Sperm meets egg. Now, scientists are a step closer to understanding the climax of this eternal love story: how sperm and egg merge to create a brand new individual. “It’s really the defining moment in an organism,” says William Snell, a biologist at the University of Texas Southwestern Medical Center in Dallas, Texas, who headed one of the teams that made the find. Snell, along with a group in Britain, discovered that a protein called HAP2 is involved...