Question

Give appropriate terms for the process of fusion of ovum and sperm.

Answer 1

The fusion of male and female gametes is the most important step in the process of sexual reproduction which results in the formation of a zygote, or fertilized egg, initiating prenatal development. Fertilization is the term used to describe the process of fusion of ovum and sperm.

Complete answer:
- Fertilization is a process in which paternal sperm and maternal egg fuse together to give rise to a primary embryo cell, often referred to as a zygote.
- In humans, during copulation semen is released by the penis into the vagina, a process referred to as insemination. Sperms move in the liquid medium by the female genital tract with the help of prostaglandins present in the semen.
- Simultaneously, its capacitation occurs, which involves the removal of membrane cholesterol present over the acrosome, dilution of decapacitation factors, and entry of ca2+ into the sperms causing rapid whiplash movement of the tail part.
- As it reaches the ampullary-isthmic junction, the ovum should be present there for them to undergo fertilization. The ovum is arrested in the secondary oocyte stage and travels to this site by the ciliary motion of the oviduct lining.
- A number of sperms adhere to the egg surface, releasing sperm lysins (Hyaluronidase, Corona penetrating enzyme, Zona lysin/Acrosin) to get through the walls of the ovum. Contact of acrosome stimulates the development of an outgrowth by the oocyte called fertilization cone.
- As the sperm head comes in contact with the fertilization cone, depolarization of the ovum membrane, calcium ion influx, zona reactions, and cortical reactions block polyspermy.
- Entry of sperm into the ovum induces completion of the meiotic division of the secondary oocyte and results in the formation of a diploid zygote.

Note: The actual fusion of gametes is called syngamy whereas fertilization includes all the events that ultimately lead to syngamy. The result of syngamy and fertilization is the formation of a diploid zygote which is the vital link that ensures continuity of species between organisms of one generation to the next generation.