The union of ovum and sperm is called fertilization.

Normally, fertilization takes place in the outer one-third of the fallopian tube shortly after ovulation (the discharge of ovum from the mature follicle) and insemination (introduction of the male’s seminal fluid into the female’s vagina).

a. Zygote. To penetrate the ovum, the sperm releases the enzyme hyaluronidase that makes the surface of the ovum more permeable.

The sperm enters the ovum. The nuclei of the sperm and the ovum fuse, making the process of fertilization complete. A new cell, called the zygote, has been made. The zygote cell has 46 chromosomes and all the potentials of the new individual: sex, size, hair color, eye color, etc.

b. Cell Divisions. The zygote begins mitotic cell divisions within the space of hours after the zygote has formed. As a result of these divisions, this new zygote cell is soon a fluid-filled ball of cells.