You are likely to have ovulated and your unfertilized egg now begins its journey. Once it has been released by the ovary, the egg is swept up by one of your fallopian tubes and, moving in the direction of the uterus, comes to rest in the widest portion of the tube, awaiting fertilization.
It is no exaggeration to say that for each sperm released the chance of even reaching the site of fertilization is in the order of one in a million. Around 300 sperm reach the tube but only one will fertilize the egg. Once the sperm has penetrated, it triggers a reaction that makes the surface impenetrable. Each sperm and egg contain 23 chromosomes, half of the total genetic material required. The egg will always contain an X chromosome but the sperm will carry either an X or Y chromosome and therefore determines the sex of the embryo. The sperm and egg chromosomes combine forming the "zygote" and fertilization is complete.