THE STRUCTURE OF MAMMALIAN GAMETES

The mammalian gametes are male gametes called sperm or spermatozoa (singular = spermato-zoon), while the female gametes are called eggs or ova (singular = ovum)

The reproductive sex cells are also known as gametes. The formation of gametes or gametogenisis takes place in the gonads.

 

Male Gametes

The male sex cells or gametes called sperms are produced in the testes by a process called spermatogenesis. The gamete is unicellular in nature.

The sperm or spermatozoon consists of a head which contains the nucleus, a middle piece and a whip-like tail or flagellum. A human sperm is about 0.05mm long and microscopic and is usually smaller than the egg (ovum).

The sperm cells are produced in the testis(es) or seminiferous tubules and stores temporarily in the epididymis

Structure and Function of Sperm Cell The structure of the sperm cell enables it to function effectively in fertilization in the following ways.

1. Acrosome: Acrosome is located at the anterior end of the head which contains lytic enzymes or agents used to dissolve the egg membrane or it enhances penetration of the egg during fertilization.
2. Middle piece: The middle piece contains numerous mitochondria which generates the energy used by the sperm cell to swim towards the egg.
3. Long whip-like tail or Flagellum: It is found at the posterior end of the sperm cell. It helps to move or propels the sperm cell.
4. Nucleus: This is found in the head of the sperm cell and contains genetic materials which fuses with the nucleus of the egg or ovum.

 

Female Gametes

The female sex cells or gametes called the eggs or ova are produced in the ovaries by a process called oogenesis. The human female gametes are larger than the sperms. Each ovum is about 0.1 mm in diameter. It consists of the cytoplasm, a nucleus in the centre, granules and yolk droplets. The yolk provides a source of nourishment for the embryo, especially at the early stages of development.

The ovum’s cytoplasm is surrounded by two membranes. The outer one is called the vitelline membrane while the inner one is the plasma membrane. The ovum is surrounded on the outside by a jelly coat of variable thickness made of glycoprotein. The nuclei of the sperm and ovum contain chromosomes (thread-like materials) which carry the genes. The genes are responsible for the transmission of characteristics from parents to offspring.

 

Differences between Sperm and Egg

 

Sperm

1. It is motile or active.
2. It has smaller cytoplasm.
3. Food reserves/yolk is is absent.
4. It is not visible to the naked eyes.
5. There is presence of head.
6. Tail or flagellum is present.
7. There is absence of vitelline membrane.

 

Egg

1. It is not motile.
2. It has larger cytoplasm.
3. Food reserves/yolk present.
4. It is visible to the naked eye.
5. Head is not present.
6. Tail or flagellum is absent.
7. Vitelline membrane is present.