<P> The process of fertilization involves a sperm fusing with an ovum . The most common sequence begins with ejaculation during copulation, follows with ovulation, and finishes with fertilization . Various exceptions to this sequence are possible, including artificial insemination, in vitro fertilization, external ejaculation without copulation, or copulation shortly after ovulation . Upon encountering the secondary oocyte, the acrosome of the sperm produces enzymes which allow it to burrow through the outer jelly coat of the egg . The sperm plasma then fuses with the egg's plasma membrane, the sperm head disconnects from its flagellum and the egg travels down the Fallopian tube to reach the uterus . </P> <P> In vitro fertilization (IVF) is a process by which egg cells are fertilized by sperm outside the womb, in vitro . </P> <P> The sperm binds through the corona radiata, a layer of follicle cells on the outside of the secondary oocyte . Fertilization occurs when the nucleus of both a sperm and an egg fuse to form a diploid cell, known as zygote . The successful fusion of gametes forms a new organism . </P> <P> Where the spermatozoon is about to pierce, the yolk (ooplasm) is drawn out into a conical elevation, termed the cone of attraction or reception cone . Once the spermatozoon has entered, the peripheral portion of the yolk changes into a membrane, the perivitelline membrane, which prevents the passage of additional spermatozoa . </P>

All cells in the human body are derived from the same fertilized ovum