Question

Define Oogenesis. Briefly describe the process of Oogenesis with the help of labelled diagram.

Hint:

Unlike spermatogenesis, which starts at puberty, oogenesis is initiated during embryonic development but is only completed if fertilization occurs.

Answer 1

Step 1: Oogenesis begins during the fetal stage where millions of oogonia are formed within each fetal ovary; no more oogonia are formed or added after birth.
Step 2: These cells enter meiosis I and get temporarily arrested at the prophase-I stage, called primary oocytes. Each primary oocyte is surrounded by granulosa cells to form a primary follicle.
Step 3: At puberty, a primary oocyte completes its first unequal meiotic division, resulting in a large haploid secondary oocyte and a tiny first polar body.
Step 4: The secondary oocyte undergoes meiosis II only upon the entry of a sperm, resulting in a large ootid (ovum) and a second polar body.