Question

Extrusion of second polar body from egg nucleus occurs
A) After entry of sperm before completion of fertilization
B) After completion of fertilization
C) Before entry of sperm
D) Without any relation of sperm entry

Answer 1

Oogenesis is the process by which female gametes are formed. The female gamete is ovum which is also known as egg.

Complete answer:
Let us first know a little bit more about oogenesis before we find the correct answer. Oogenesis is a part of gametogenesis which occurs in females.
Oogenesis is a part of gametogenesis which occurs in females.

The process of oogenesis takes place in the outermost layer of ovaries and has three stages,

1. Prenatal
2. Antral
3. Pre-ovulatory

Option A: Once the sperm enters the ovum it leads to a meiotic split of the secondary oocyte. The entry of the sperm into the cytoplasm of ovum is facilitated by acrosomal secretions. Similar to the first meiotic division, even the second meiotic division is unequal and results in the formation/ extrusion of a second polar body. Therefore, this is the correct option.
Option B: Once the fertilization is completed, zygote is formed and prior to that extrusion of a second polar body from the egg nucleus occurs. Therefore, this is the incorrect option.
Option C: Before the entry of sperm, the ovum does not undergo any changes which can lead to extrusion of the polar body from the egg nucleus. If fusion of egg and sperm does not occur, then in that case, the egg is not implanted and the woman's body sheds the egg. Therefore, this is the incorrect option.
Option D: Only when sperm enters the ovum extrusion of the polar body from the egg nucleus. If there is no entry of sperm, the female body sheds the egg. Therefore, this is the incorrect option.

Thus, the correct option is (A) After entry of sperm before completion of fertilization.

Note: Fertilization is the process by which the egg and sperm fuses and gives rise to a zygote. By the time fertilization takes place, meiosis II occurs which gives rise to a third polar body. In case, fertilization does not occur, then oocyte degenerates.