Question

Extrusion of second polar body from egg nucleus occurs
A. After entry of sperm and before completion of fertilisation
B. After completion of fertilisation
C. Before entry of sperm
D. Without any relation with sperm entry

Answer 1

Fertilization is a natural life process that involves the union of male and female gametes, resulting in the development of a zygote. In humans, the fallopian tube is where fertilisation takes place.
Thousands of sperms are inseminated into the female vagina during this process. The sperms go towards the uterus and eventually reach the fallopian tube's opening. Only a small percentage of sperm will make it to the fallopian tube's entrance.

Complete answer:
Option A: After sperm enters the egg nucleus, but before fertilisation, the second polar body extrudes from the nucleus. The introduction of sperm into the ovum causes the secondary oocyte's meiotic division to be completed.
When sperm enters the body, the metaphase promoting factor (MPF) is broken down, and the anaphase promoting complex is activated (APC).
So, option A is correct.
Option B: The production of the acrosome aids sperm entry into the cytoplasm of the ovum during fertilisation. The secondary oocyte's second meiotic division is completed as a result of this. A second polar body and a haploid ovum are formed during the second meiotic division.
So, option B is incorrect.
Option C: The introduction of sperm into the ovum causes the secondary oocyte's meiotic division to be completed. The breakdown of metaphase promoting factor and the activation of the anaphase promoting complex are both caused by sperm entering the cell.
So, option C is not correct.
Option D: When sperm reaches the ovum, the secondary oocyte is able to ‘meiotic split.' The sperm entry causes the metaphase stimulating factor to break down, and the sperm subsequently begins fertilisation. The fertilisation process affects oocyte activation, which results in a second polar body ejection.
So, option D is not correct.

So, the correct answer is “Option A”.

Note:
Steps of fertilisation in humans-
1. Acrosomal reaction
2. Cortical reaction
3. Sperm entry
4. Karyogamy
5. Activation of eggs
6. Implantation
7. Sex determination