Oogenesis

Oogenesis is the formation of ovum from oogonial cells that are formed in the ovary from primordial germ cells. And as in spermatogenesis it involves meiosis to produce haploid ovum. You have learnt in the section on spermatogenesis that the differentiation of sperm occurs after the meiotic events. In oogenesis the process of first meiotic division is very prolonged; and it is during this process that growth and differentiation of oocyte take place. In many animals most events related to oocyte differentiation occur during prophase I of first meiotic division. In animals which produce yolk-laden eggs, this phase is divided into

• Previtellogenesis (before yolk production)
• Vitellogenesis (yolk deposition)
• Post Vitellogenesis (after yolk deposition)