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

# OOGENESIS Oogenesis is the process of formation of the female gamete, the ovum. In female, oogenesis starts in the embryonic stage and gets computed 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 phase occurs in the embryonic stage itself. The primordial germ cell originates in the yolk sac in the early embryo and then migrates to the primitive ovary, when it transforms into germ cells called oogonia, which are not completely developed. Oogonia is diploid and undergoes mitosis, which increases the number and forms more oogonia that constitute the multiplication phase. ## Phase of Growth In this phase, oogonia differentiate and transform into diploid primary oocytes. This phase also occurs in the embryonic stage itself, wherein all oogonia are transformed into primary oocytes. Since primary oocytes are differentiated, they cannot undergo mitosis, so no more oogonia can be added after birth. This is the major reason why oogenesis can occur only until a limited period in the life of a female. ## Phase of Maturation This phase of meiosis also starts in the embryonic period but is completed only during fertilization. In the embryonic stage itself, primary oocytes enter meiosis I but are unable to complete it. They get arrested in prophase I.