Question

Extrusion of the second polar body from the egg nucleus occurs:

• A. After entry of sperm but before fertilization
• B. After completion of fertilization
• C. Before entry of sperm into the ovum
• D. Simultaneously with first cleavage

Hint:

In humans, meiosis II in the secondary oocyte is completed only after sperm entry, which leads to the formation of the second polar body.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question concerns the timing of the completion of Meiosis II in the female gamete during the process of reproduction.
Step 2: Detailed Explanation:
In human females, the primary oocyte completes Meiosis I just before ovulation, forming a secondary oocyte and the first polar body.
The secondary oocyte starts Meiosis II but is arrested at the Metaphase II stage.
Meiosis II is completed only when a sperm penetrates the zona pellucida of the ovum.
The entry of the sperm induces the completion of the meiotic division of the secondary oocyte.
This results in the formation of an ootid (haploid ovum) and a second polar body.
This occurs after the sperm has entered the egg cytoplasm but before the fusion of the male and female nuclei (karyogamy/fertilization).
Step 3: Final Answer:
The extrusion happens after sperm entry but before the actual completion of fertilization.