Before a zygote is formed, there must be an ovum or an egg cell (Biology Online). Ovulation, occurring once a month, is a process where the ovary releases an egg into the fallopian tube. If fertilization occurs, then the egg will move onto the next steps of pregnancy (Iowa State University Digital Press). If no fertilization occurs, then menstruation occurs. Also known as menstrual period, it is the process in which the uterus sheds its blood lining when pregnancy does not occur (MedlinePlus).