In humans females at the time of birth, the stage of cell cycle of oocyte is :
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Prophase-I
Option (1) Prophase-I — Correct. Oogenesis starts in the foetus. The oogonia begin meiosis and stop in prophase-I; these cells are the primary oocytes. A girl is born with them in this arrested state.
Option (2) Prophase-II — Incorrect. Meiosis I is completed only at puberty, inside the growing follicle. Only then does the secondary oocyte form.
Option (3) Meiosis-II — Incorrect. Meiosis II is completed only when a sperm enters the ovum, at fertilisation.
Option (4) Mitosis — Incorrect. Mitosis forms the oogonia in the foetus. By birth the cells are no longer dividing by mitosis, and no new oogonia are added.
NCERT Extract:
Gametogenesis – “… The process of formation of a mature female gamete is called oogenesis which is markedly different from spermatogenesis. Oogenesis is initiated during the embryonic development stage when a couple of million gamete mother cells (oogonia) are formed within each fetal ovary; no more oogonia are formed and added after birth. These cells start division and enter into prophase-I of the meiotic division and get temporarily arrested at that stage, called primary oocytes.”