Oogenesis:
It is the process by which the mature ovum is formed in the ovary.
Stages of Oogenesis:
Fetal Oogenesis:
Phase I: The primitive germ cells of the ovary divide mitotically producing oogonia. These oogonia are stem cells that proliferate by mitosis to form primary oocytes.
Phase II: Primary oocytes from the oogonia enter a prolonged prophase of the first meiotic division and remain in this stage until ovulation occurs after puberty. These primary oocytes are now covered by single granulosa cell layers thus forming primordial follicles.
Pubertal Oogenesis:
Phase I: During this phase, the primary oocytes are in the prophase of the first meiotic division since fetal life completes the 1st meiotic division, thus forming secondary oocytes and 1st polar body formed.
Phase II: Now secondary oocytes immediately begins the second meiotic division but this division also stops at metaphase and is completed only if fertilization occurs. During this time the second polar body is formed along with a mature ovum. This second polar body undergoes atresia, and the mature ovum is involved in fertilization.