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Manimegalai Ramasamy: Life Cycle of an Oocyte
Photo: DepositPhotos
Aug 25, 2026, 19:09

Manimegalai Ramasamy: Life Cycle of an Oocyte

Manimegalai Ramasamy, Senior Clinical Embryologist at Nova IVF Fertility, shared on LinkedIn:

“Life cycle of an oocyte – simple explanation

The oocyte is the female reproductive cell that develops in the ovary. Its development occurs in several stages:

1. Fetal life – Oogonia

  • Before birth, oogonia (2n) multiply by mitosis.
  • They develop into primary oocytes.
  • Primary oocytes begin meiosis I but stop at prophase I.

2. Childhood – Primary oocyte

  • Primary oocytes remain arrested in prophase I throughout childhood.
  • They are surrounded by supporting follicular cells inside the ovary.

3. Puberty – Meiosis resumes

  • From puberty onward, during each menstrual cycle, some primary oocytes resume meiosis I.
  • Usually one becomes the dominant oocyte.
  • Meiosis I produces:
  • Primary oocyte – Secondary oocyte + first polar body
  • The secondary oocyte is haploid (n).

4. Ovulation

  • The secondary oocyte is released from the ovary.
  • It begins meiosis II but stops at metaphase II.
  • This is the cell that can be fertilized.

5. If fertilization occurs

  • Entry of a sperm triggers completion of meiosis II.
  • The secondary oocyte becomes the mature ovum, and a second polar body is formed.
  • The genetic material from the oocyte and sperm then contributes to formation of the zygote.

6. If fertilization does not occur

  • The secondary oocyte does not complete meiosis II and eventually degenerates.”

Manimegalai Ramasamy

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