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## OOGENESIS Oogenesis is the process of formation of female gamete; ovum. In female, oogenesis starts in the embryonic stage and gets completed during fertilization. Unlike spermatogenesis, oogenesis ceases at the age of around 50, when menopause arises. Oogenesis is divided into the following pha...

## OOGENESIS Oogenesis is the process of formation of female gamete; ovum. In female, oogenesis starts in the embryonic stage and gets completed during fertilization. Unlike spermatogenesis, oogenesis ceases at the age of around 50, when menopause arises. Oogenesis is divided into the following phases: ### Phase of Multiplication This occurs in the embryonic stage itself. - Bimordial germ cell originates in the yolk sac in early embryos and then migrate to the primitive ovary, when it transforms into germ cells called oogonia (not completely developed). - Oogonia is diploid and undergo mitosis. It increases in number and forms more oogonia which constitute the multiplication phase. ### Phase of Growth - In this phase, oogonia differentiate and transform into diploid primary oocyte. - This phase also occurs in the embryonic stage itself wherein all oogonia are transformed into primary oocytes. - Since primary oocyte is differentiated and cannot undergo mitosis, no more oogonia can be added after birth. - This is the major reason why oogenesis can occur only till a limited period in the life of a female. ### Phase of Maturation - It is the phase of meiosis which also starts in embryonic period, but gets completed only during fertilization. - In the embryonic stage itself, primary oocytes enter into meiosis I but cannot complete it. They get arrested in prophase I.