<Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> Human fertilization is the union of a human egg and sperm, usually occurring in the ampulla of the fallopian tube . The result of this union is the production of a zygote cell, or fertilized egg, initiating prenatal development . Scientists discovered the dynamics of human fertilization in the nineteenth century . </P> <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>

What do we call the moment when the sperm and ovum join