Concerning maturation of the female gamete (oogenesis), when do the oogonia enter meiosis I and undergo DNA replication to form primary oocytes?
All primary oocytes are formed by month 5 of fetal life, so no oogonia are present at bih. Oogonia enters meiosis I before bih. Hence at bih, ovary contains primary oocytes arrested in the diplotene stage of prophase I which gets completed after pubey to form secondary oocyte. This secondary oocyte is arrested in metaphase-2 stage of meiosis II which is completed when feilization occurs. 3rd month end 5th month 7th month Oogonia are arranged in clusters surrounded by a layer of epithelial cells. Number of germ cells in ovary reaches maximum (7 million) Majority of oocyte degenerate, except few, surviving ones enter prophase I & are surrounded by follicular epithelial cells forming PRIMORDIAL FOLLICLE.
During fetal life
At bih
At pubey
With each ovarian cycle
General Embryology 2