Question

Draw a flowchart to represent the process of oogenesis.

Hint:

Remember that the "arrest" points are crucial: Prophase I (from birth to puberty) and Metaphase II (until fertilization).

Answer 1

Step 1: Understanding the Concept:
Oogenesis is the process of formation of a mature female gamete (ovum). Unlike spermatogenesis, it begins during the embryonic development stage.

Step 2: Detailed Explanation:
1. Fetal Life: Oogonia (\(2n\)) multiply by mitosis. They enter Meiosis I and get arrested at the Prophase I stage, becoming Primary Oocytes.
2. Puberty: A primary oocyte completes its first meiotic division, which is unequal. This results in a large haploid Secondary Oocyte (\(n\)) and a tiny First Polar Body (\(n\)).
3. Ovulation: The secondary oocyte is released from the ovary. It starts Meiosis II but gets arrested at the Metaphase II stage.
4. Fertilisation: The entry of a sperm triggers the completion of Meiosis II. This is again an unequal division, resulting in a mature Ovum (\(n\)) and a Second Polar Body (\(n\)).

Step 3: Final Answer (Flowchart):
\[ \text{Oogonia (2n)} \xrightarrow{\text{Mitosis / Differentiation}} \text{Primary Oocyte (2n)} \]
\[ \downarrow (\text{Meiosis I starts in fetal life, arrested in Prophase I}) \]
\[ \text{Primary Oocyte (2n)} \xrightarrow{\text{Meiosis I completed at Puberty}} \text{Secondary Oocyte (n)} + \text{1st Polar Body (n)} \]
\[ \downarrow (\text{Meiosis II starts, arrested in Metaphase II}) \]
\[ \text{Secondary Oocyte (n)} \xrightarrow{\text{Entry of Sperm / Fertilisation}} \text{Ovum (n)} + \text{2nd Polar Body (n)} \]