Gametogenesis

Introduction

The generation of gametes from haploid progenitor cells is called gametogenesis. Different differentiation programs produce two morphologically distinct gametes in mammals and higher plants. The germline is a tissue produced by animals devoted to forming gametes. Germ cells are individual germline cells. A Germ cell goes through meiosis during gametogenesis and produces haploid cells that grow into gametes.

Due to this, meiosis is an essential aspect of gametogenesis in animals. Gametogenesis and meiosis are separated in plants, fungi, and algae. Diploid cells go through meiosis to create haploid spores, which produce a haploid generation known as a ‘gametophyte.’ Gametes emerge from cells in the latter, sometimes in reaction to environmental or chemical stimuli. 

Many unicellular and multicellular eukaryotes produce gametes through haploid cells a few generations after meiosis or even soon after some species. Fungi, multicellular algae, and some protists have gametes that are not morphologically diverse and thus are termed (+) or (–) rather than egg or sperm.

The mechanism through which diploid precursor cells undergo meiotic division to generate haploid gametes is known as gametogenesis. 

• This process is known as spermatogenesis in males, and it results in spermatozoa (sperm)

• This process is known as oogenesis in females, and it results in the production of ova (eggs)

The following processes are involved in the gametogenesis process, which takes place in the gonads:

• Precursor germ cells go through multiple mitotic divisions & grow

• To form haploid daughter cells, two meiotic divisions are required

The haploid daughter cells are differentiated to create functioning gametes.

Gametogenesis Definition

To define gametogenesis, it is the biologic process that occurs in live organism cells that results in the formation of gametes. The species’ reproduction would be possible thanks to gamete transfer, which occurs when the organisms reach a particular stage of development.

When cells undergo meiosis to produce gametes, this is called gametogenesis. So, what exactly are gametes? They’re the cells that allow an organism to reproduce. To be precise, gametogenesis & reproduction are two distinct processes with very different meanings.

Meaning of Gametogenesis

In living organisms, the gametogenesis procedure involves the development of reproductive cells or sex cells. It takes place in plants via mitosis, while it takes place in mammals via meiosis. During gametogenesis, the two primary phases are the development of male gametes and female gametes.

Gametogenesis takes place in the following ways, depending on the live organism:

• Plants: It occurs when diploid gametocytes undergo meiotic division. It occurs in higher plants in tandem with sporogenesis

• Animals: It occurs in animals through meiosis, in which gametes are produced from diploid mother cells found in gonads

Stages of Gametogenesis

There are three stages to the gametogenesis process. Mitotic divisions and cell development of precursor germ cells are two of them.

• Meiosis I & Meiosis II occur to produce haploid daughter cells

• For the formation of functional gametes, haploid daughter cells are differentiated

The creation of male and female gametes is dependent on these phases.

Gametogenesis in Humans

The division of diploid cells into new haploid cells is known as gametogenesis. There are two types of gametes found in humans. The male gametes are sperm, and the female gametes are the ovum.

• Spermatogenesis is the process of producing sperm
• Oogenesis is the creation of an ovary

Spermatogenesis

Immature germ cells are formed in the testes of males. The mechanism of spermatogenesis transforms these immature germ cells, or spermatogonia, into sperms in males throughout puberty. Spermatogonia are diploid cells that divide during mitosis and multiply in number. Meiosis occurs in primary spermatocytes, resulting in secondary spermatocytes, which are haploid cells. To create immature sperms or spermatids, these secondary spermatocytes go through a second meiotic division. These spermatids proceed through spermiogenesis to become sperms. GnRH, LH, FSH, and androgens are among the hormones that stimulate spermatogenesis.

Oogenesis

The oogonia are transformed to the mature ovum in females. Oogenesis is the name for this process. Millions of oogonia, or mother cells, are generated in the female ovary during fetal development. 

These mother cells go through meiotic cell division, which stops at prophase-I and results in the formation of primary oocytes. On the outer layer, primary oocytes are lodged within primary follicles. Secondary follicles occur when a thicker granulosa cell layer surrounds primary follicles. The tertiary follicle develops from secondary follicles. The primary oocytes in the tertiary follicles complete meiosis and divide unequally to create secondary oocytes (haploid) and the polar body during female puberty. The mature Graafian follicle is produced after the tertiary follicle experiences morphological and functional modifications. A secondary oocyte goes through a second meiotic division to generate an ovum. During the menstrual cycle, an ovum is discharged from the Graafian follicle. Ovulation is the discharge of an ovum from a Graafian follicle. The female reproductive hormone, stimulated by the pituitary gland, regulates ovulation.

Conclusion

Regular fertilization and early embryonic development require the creation of genetically competent gametes. Understanding the fundamental mechanisms in vivo will help us better reproduce this mechanism in vitro, which could help us better define and comprehend idiopathic infertility. 

The study highlights over the last few decades have not only expanded our understanding of gamete and embryo development, as well as related illnesses such as infertility and birth abnormalities, but it also holds enormous promise for the development of novel reproductive therapies.