Question

Describe the chemical and physical events of fertilization in mammals.

Answer 1

Hint: The process of fertilization involves the fusion of an ovum with sperm. The fertilization takes place in the body at a particular site called as fallopian tube or ampullary-isthmic junctions.

Complete Answer:
During fertilization various processes take place and are majorly categorized into two events i.e. physical or chemical events.
The various processes involved in chemical events are:
- Estimation of ovum and sperm, which could be performed through fertilizin-antifertilizin compatibility reactions.
- Fertilizin is a glycoprotein, obtained from egg, which interacts with the antifertilizin, composed of amino acids (acidic) of the sperms obtained from the similar species. These interactions resulted in the formation of the sperms (sticky) having greater abilities to adhere to the surface of the egg.
- The zona pellucida is degraded by the zonalysins (proteolytic enzymes) and thus enhances the passageway of sperm cells to reach the ovum.

Apart from the chemical events, various processes are observed during the physical events:
- These processes include fusion of acrosomal membrane with the plasma membrane of the sperm cells.
- Afterwards, the enzymes present in the acrosomes are diffused into the environment near the egg and sperm. Finally, the ovum gets activated when the sperms reaches the ovum and experiences the second meiotic division.
- As a consequence, the oocyte generates an ovum and a secondary polar body. The polar bodies eventually deteriorate and a haploid number of chromosomes is contained within the ovum.

Note: During the process of fertilization two major functions are observed for significant development of embryos. They are:
(a) After fertilization, the meiotic division is completed by the secondary oocytes and a second polar body is produced, which at last gets degenerated at the end of the process.
(b) As a second function, a well-developed zygote (diploid) is developed, which further goes through cleavage and forms a morula leading to the development of blastocyst.