Fertilisation
Fertilisation is the moment when a sperm and egg join together, and the genes from the mother and father combine to form a new life. For the sperm, it is the end of a long and difficult journey - the winner of a race that started out with 500 million competitors (that's more than 16,000 times the number of runners in the 2000 London marathon). The prize is the egg, which is released from the ovary and then travels along the fallopian tube to meet the sperm.
