At bih, oocytes are in which stage of development:
Ans:D.)Resting phase between prophase and metaphase of 1st meiotic division. OOGENESIS The process involved in the development of a mature ovum is called oogenesis. The primitive germ cells take their origin from the yolk sac at about the end of 3rd week and their migration to the developing gonadal ridge is completed round about the end of 4th week. In the female gonads, the germ cells undergo a number of rapid mitotic divisions and differentiate into oogonia. The number of oogonia reaches its maximum at 20th week, numbering about 7 million. While the majority of the oogonia continue to divide, some enter into the prophase of the first meiotic division and are called primary oocytes. These are surrounded by flat cells and are called primordial follicles and are present in the coex of the ovary. At bih, there is no more mitotic division and all the oogonia are replaced by primary oocytes which have finished the prophase of the first meiotic division and remain in resting phase (dictyotene stage) between prophase and metaphase. Total number of primary oocytes at bih is estimated to be about 2 million. The primary oocytes do not finish the first meiotic division until pubey is reached. At pubey, some 400,000 primary oocytes are left behind, the rest being atretic. Out of these, some 400 are likely to ovulate during the entire reproductive period.
Prophase of 1st meiotic division
Oogonia
Telophase of 2nd meiotic division
Resting phase between prophase and metaphase of 1st meiotic division