Question

When does the extrusion of the second polar body from the egg nucleus occur?

• A. Before entry of sperm
• B. During fertilization
• C. After entry of sperm but before fertilization
• D. After embryonic development begins

Hint:

Key stages in human fertilization: Primary oocyte → Meiosis I completed Secondary oocyte → Arrested in Metaphase II Sperm entry → Meiosis II completed → Second polar body released

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question focuses on the timing of the completion of meiosis II in the female gamete (oocyte).
Step 3: Detailed Explanation:
1. In human females, the secondary oocyte is arrested at the Metaphase II stage of meiosis.
2. This arrest is only broken when a sperm cell makes contact with and penetrates the zona pellucida and plasma membrane of the oocyte.
3. Upon sperm entry, the "Anaphase Promoting Complex" is activated, allowing the cell to complete meiosis II.
4. This unequal division results in the formation of the ootid (large cell) and the second polar body (small cell).
5. This event happens strictly after the sperm enters the cytoplasm but before the fusion of the male and female pronuclei (amphimixis).
Step 4: Final Answer:
It occurs after sperm entry but before fertilization (C).