Oogenesis that is formation of ovum of female gamete :

Oogenesis that is formation of ovum of female gamete :

Oogenesis starts in the ovary of the female foetus when it is in the womb of her mother. if we zoom into the female reproductive system of the foetus we can see in the ovaries of the female foetus the oogenesis has already started.

the germinal epithelial cells inside the ovary wall of the foetus starts dividing by mitotic cell division and forms oogonium. This oogonium cells goes through growth phase and forms the primary oocyte inside the ovary of the female foetus.

now the primary oocyte goes through meiosis 1 it gets arrested in prophase 1 of meiosis cell division 1 and stops here until the female foetus borns and becomes a mature woman and comes to the puberty. When it reaches the puberty inside the ovary of the matured female, the cell which got arrested in prophase 1, the primary oocyte, starts dividing again and complete the meiosis 1 and forms secondary oocyte and one polar body that is the first polar body.

now the secondary oocyte goes through Meotic2 cell division. In this process it gets arrested again in metaphase2 of meiotic cell division 2. It remains arrested until it reaches ovulation and fertilization. During ovulation the secondary oocyte is ovulated. Sperm meets the seconday oocyte and the nuclei of sperm enters in the seconday oocyte and waits for the completion of meotic 2 cell division of secondary oocyte to become ootid or ovum. During fertilization The primary oocyte completes the meotic2 cell division in presence of male pronuclei and after completing meotic2 cell division it becomes female pronuclei and fuses with the male pronuclei completing the fertilization process.

Meanwhile seconday oocyte also gives rise to a polar body and 1st polar gives rise to 2 more polar bodies.

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