Question

Which among the following is a correct statement regarding fertilisation?

• A. The entry of sperm activates the secondary oocyte for completing meiosis.
• B. Only one sperm reaches the egg and enters it.
• C. Only the acrosome of the sperm enters the egg.
• D. Two haploid nuclei fuse and immediately divide to produce two nuclei, which are again haploid.

Answer 1

The correct option is A The entry of sperm activates the secondary oocyte for completing meiosis.

Millions of sperms are released in the human female reproductive system during copulation. Although some of them are lost during the path of reaching the ovum due to the acidic environment of vagina, others undergo changes (capacitation) to fertilise the ovum. Hence many sperms reach the egg but only one sperm enters inside the egg. The nucleus of sperm along with centrioles enters the egg. Further entry of sperms is prevented due to cortical reaction.

The secondary oocyte released due to the rupture of the Graafian follicle is halted at metaphase II of meiosis II. This secondary oocyte is transported into the ampulla of the fallopian tube. The binding of sperm with the secondary oocyte triggers the activation of the secondary oocyte which now completes meiosis II and forms the haploid ovum.

The haploid nuclei of sperm and ovum fuse to form diploid zygote which is a single cell with a single diploid nucleus.