GAMETOGENESIS- SPERMATOGENESIS AND OOGENESIS

Gametogenesis is a scientific study by which diploid or haploid blast cells goes under cell division and differentiation to form mature haploid sex cells. Depending on the biological life cycle of the organism, the gametogenesis occurs by meiotic division of diploid Gametocytes in several gametes.

For example, in gametophytes, plants produce gametes through mitosis. After sporic meiosis, the gametophytes grow from haploid spores. The existence of a multicellular, haploid phase in the life cycle between meiosis and gametogenesis is also referred to as alternation of generations.

In simple language, it is the process by which sperms (male sex cells) and ova (female sex cells) are designed in the male testes and female ovaries respectively. These gametes are different from all the other cells present in the body. It is because their nuclei contain half the count of chromosomes present in nuclei of somatic cells.

Gametogenesis which refers to the formation of sperms is called spermatogenesis. Gametogenesis which refers to the formation of ova is termed as oogenesis.

SPERMATOGENESIS

Spermatogenesis is the process by which haploid spermatozoa, a motile sperm cell develops from germ cell in the seminiferous tubules of the testis. This process starts with the division of the stem cells by the process of meiosis. It is located close to the lower membrane of the tubules. These cells are called spermatogonial stem cells. Two types of cells are produced during the mitotic division.

Type A cells restore the stem cells whereas type B cells transform into primary spermatocytes. The primary spermatocyte divides by the process of meiosis I into two secondary spermatocytes; each secondary spermatocyte divides into two equal haploid spermatids by meiosis II. The spermatids are transformed into sperm by the process of spermiogenesis. These develop into mature sperms, also known as spermatozoa. 

Creation of Spermatids

Three stages of procedure covers are as follows:

Multiplication Phase: During sexual maturity, due to mitosis, the division of unseparable primordial germ cells occurs many times. This is to produce a large count of spermatogonia. Type A and type B are its two kinds. Type A spermatogonia act as the stem cells that split to make additional spermatogonia. On the other side, Type В spermatogonia can be assumed as the prototypes of male sex cells.

Growth Phase: Every type В spermatogonium rapidly grows to create a major primary spermatocyte through nourishment received from the nursing cells. This phase further ends in the maturation stage.

Maturation Phase: Under this phase, primary spermatocyte experiences two back to back divisions and are termed as maturation divisions, and the first maturation disunion is the meiotic division. Therefore, the primary spermatocyte splits into two haploid daughter cells known as secondary spermatocytes. Further, both the secondary spermatocytes go through second maturation separation that is a regular mitotic division which leads to the creation of four haploid spermatids.

OOGENESIS

Oogenesis is the differentiation of the ovum or egg cell into a cell which has the ability to further develop when fertilised. It is developed from the primary oocyte by maturation. Oogenesis begins in the embryonic stage. Oogenesis starts with the process of developing primary oocytes, which occurs through the change of small diploid cell, known as oogonia into primary oocyte and it is a process called oocytogenesis. 

From one single oogonium, only one mature oocyte will rise, with three other cells called polar bodies. The process of oocytogenesis is complete either before or shortly after birth. It is commonly assumed that, when oocytogenesis is complete, no additional primary oocytes are made, unlike to the male process of spermatogenesis, where gametocytes are continuously created.

Creation of Oocytes

The three phases to understand the creation of oocytes are as follows:

Multiplication Phase: During foetal development, it is observed that certain cells are bigger than other cells present in the germinal epithelium of the female ovary. Hence, these cells divide themselves by the process mitosis, creating a pair of million oogonia or mother egg cells in each ovary present in the foetus. After birth, there are no more oogonia which can be formed or augmented.

Growth Phase: This is the longest phase of the primary oocyte. In this, the oogonium develops into bigger primary oocytes. After this, every primary oocyte gets bounded by a granulosa cell layer to make the primary follicle. Afterwards, a large number of follicles get despoiled during the period from birth to puberty. Therefore, at puberty almost around 60,000 to 80,000 primary follicles can be found in each ovary.

Maturation Phase: Similar to a primary spermatocyte, every primary oocyte practises two maturation divisions. However, the results of maturation divisions under oogenesis are quite unique to those which occur in spermatogenesis. Taking into consideration the first meiotic division, the primary oocyte divides into two uneven haploid daughter cells which are known as the large secondary oocyte and a small polocyte.

DIFFERENCES BETWEEN SPERMATOGENESIS AND OOGENESIS

Nature of the process: Spermatogenesis is the male version of gametogenesis which results in the formation of mature male gametes whereas oogenesis is the female version of gametogenesis which results in the formation of mature male gametes.

Occurrence: Spermatogenesis occurs in the testes until the sperm moves to the epididymis and gains motility whereas oogenesis occurs in the ovary until the mature ovum moves to the fallopian tube.

Rate of production: Spermatogenesis forms millions of sperms every day whereas oogenesis releases one ovum per month.

Continuity of the process: Spermatogenesis is a continuous process that begins with puberty and continuous until death whereas oogenesis begins in the fetal stage while the rest continue after puberty till menopause.

Starting cell: Spermatogenesis starts in the primary spermatocyte whereas oogenesis is the primary oocyte.

Growth phase: Spermatogenesis has a shorter growth phase than in oogenesis.

Resting phase: There is no resting phase during the spermatogenesis process whereas the resting phase occurs during oogenesis from the embryonic stage till puberty.

Size of the gametes: In spermatogenesis, the male gametes formed are smaller in size than the female gametes whereas in oogenesis, the female gametes formed are larger in size than the male gametes.

CONCLUSION

We have discussed gametogenesis as the process by which sperms and ova are designed in the male testes and female ovaries respectively. Spermatogenesis is the process by which haploid spermatozoa, a motile sperm cell develops from germ cell in the seminiferous tubules of the testis. Oogenesis is the differentiation of the ovum or egg cell into a cell which has the ability to further develop when fertilised.