Question

Give a brief account of oogenesis.

Answer 1

The process of oogenesis occurs in three phases:

1. Multiplication phase:
   1. The primordial germinal cells (oogonia, 2n) divide repeatedly by mitosis to form a large number of oogonia.
   2. This occurs during embryonic development.
2. Growth phase:
   1. Some oogonia grow in size and form primary oocytes (2n).
   2. Cell organelles like ER, mitochondria, and Golgi apparatus multiply.
3. Maturation phase:
   1. Each primary oocyte (2n) undergoes meiosis I to form a secondary oocyte (n) and a small first polar body (n).
   2. The secondary oocyte begins meiosis II but is arrested at metaphase II.
   3. The secondary oocyte is released at ovulation and completes meiosis II only if fertilization occurs.
   4. This results in a mature ovum (n) and a second polar body (n).