Question

During which of the following steps does extrusion of second polar body from egg nucleus occur?

Options

• After fertilization

• Simultaneously with first cleavage

• After entry of sperm but before fertilization

• Before entry of sperm into ovum

Answer 1

After entry of sperm but before fertilization

Explanation:

The penetration of a secondary oocyte by a sperm cell, the meiotic division of the secondary oocyte to generate an ovum, and the subsequent union of the nuclei of the gametes are all part of fertilisation. 

After sperm enters the egg nucleus, but before fertilisation is completed, the second polar body extrudes from the nucleus.

When sperm enters the cell, the metaphase promoting factor (MPF) breaks down 
and switches on.