Question

What is Oogenesis. Briefly describe the process of Oogenesis.

Hint:

Critical Arrest Points:
1. Prophase I (Before birth).
2. Metaphase II (At ovulation, until sperm arrival).

Answer 1

Step 1: Understanding the Concept:
Oogenesis is markedly different from spermatogenesis. While males produce sperm continuously from puberty, females are born with all the potential eggs they will ever have.
Step 2: Detailed Explanation:
The process follows a strict chronological timeline:
1. Fetal Period: Gamete mother cells (oogonia) multiply by mitosis in the fetal ovary. They enter Meiosis I but get arrested at the Diplotene stage of Prophase I. These are now "Primary Oocytes."
2. Childhood: Primary oocytes remain dormant inside primary follicles. Many of these follicles degenerate (follicular atresia) until puberty.
3. Puberty to Menopause: Every month, a few primary follicles begin to mature. One becomes the dominant Graafian follicle.
4. First Meiotic Division: Just before ovulation, the primary oocyte completes Meiosis I. This division is unequal, producing one large Secondary Oocyte (carrying most of the cytoplasm) and one tiny First Polar Body.
5. Ovulation: The secondary oocyte is released from the ovary. It is arrested again at Metaphase II.
6. Completion: Meiosis II is completed ONLY if a sperm enters the secondary oocyte. This produces the mature Ootid (Ovum) and a second polar body.
Step 3: Final Answer:
Oogenesis is the developmental process that produces a haploid ovum from diploid oogonia through a series of mitotic and meiotic divisions, characterized by significant periods of arrest.