Explanation
Extrusion of the second polar body from the egg nucleus occurs after entry of sperm before completion of fertilization. The process of meiosis in human females produces a secondary oocyte, which is arrested in metaphase of meiosis II. At the time of fertilization, the sperm enters the secondary oocyte, triggering the completion of meiosis II and the extrusion of the second polar body.
The second polar body is a small, non-functional cell that contains half the number of chromosomes as the original cell. Its extrusion allows for the fusion of the haploid sperm and haploid egg nuclei, forming a diploid zygote with the full complement of chromosomes.
Option A is correct as it correctly describes the timing of the extrusion of the second polar body.
Option B is incorrect as the extrusion of the second polar body occurs before completion of fertilization.
Option C is incorrect as the secondary oocyte is already formed through meiosis before the entry of sperm.
Option D is incorrect as the extrusion of the second polar body is directly related to the entry of sperm and the completion of meiosis II.
