An oocyte is a young egg (an immature ovum). Oocytes mature within a follicle. These follicles are situated on the ovaries’ outer layer. Several follicles form during each reproductive cycle. Each cycle, just one oocyte will mature into an egg and be ovulated from its follicle. This procedure is known as ovulation. The process of producing a mature female gamete is known as oogenesis (ovum). It expresses itself in the female reproductive system’s ovaries. Oogenesis is a one-way process that begins before conception, ends in the middle, and continues after menarche. During oogenesis, a diploid oogonium, also known as an egg mother cell, develops and turns into a diploid primary oocyte. The initial meiotic division, also known as reductional division, begins in this diploid primordial egg, culminating in the development of two unequal haploid cells.

Process of Oocyte formation

• These cells migrate into the developing embryo’s testis or ovaries (also known as the gonads). When the primordial germ cell enters the gonads, it is influenced by the surrounding cells and transforms into oogonium (plural, oogonia). 
• Oogonia is composed of diploid cells. This means that they have two (di) sets of chromosomes. In a human cell, there are 23 pairs of these, for a total of 46. During the first five months of pregnancy, the oogonium multiplies through a process known as mitotic cell division. During mitotic cell division, the oogonium divides into two cells, each of which contains: They only have half of a chromosomal set, or 23 chromosomes. (These are referred to as haploid cells.)
• Every oogonium that splits produces a distinct sister cell with its own set of chromosomes. This indicates that no two oogoniums have the same chromosomal structure.
• Because of this mitotic division, each new creature has a genetic make-up that is distinct from everyone else’s. Meiosis is a process that only germ cells go through. This mutation is seen only in immature egg and sperm cells. 
• Each egg will go through two meiotic cell divisions before becoming a mature ovum. Rather than creating new oocytes, the oocyte expands and matures as a result of meiotic cell division.
• At the end of foetal development, oocytes stop multiplying and begin to mature.
• At this moment, they are undergoing their initial meiotic cell division. Unlike the oogonium, this cell division results in oocyte growth rather than more oocytes. They do not, however, simply speed through development to maturity right now.
• Primary oocytes freeze in the early stages of development and remain frozen until reproductive hormones signal the next phase.
• During puberty, oogenesis will continue. Puberty causes the next step of oocyte maturation. Of course, not all oocytes will progress to the latter stages of oocyte development at the same time. They alternate during a woman’s reproductive years. Every month, a new batch of primary oocytes matures. 
• After being influenced by reproductive hormones, a primary oocyte completes Stage I of meiotic cell division. This is referred to as oocyte maturation. At the completion of this first step of meiotic cell division, the cell divides into two different cells: a small polar body and a large secondary oocyte. The little polar body deteriorates over time. The maturation of the secondary oocyte progresses to the next step. 
• The oocyte is currently in the second stage of meiotic cell division. The secondary oocyte will eventually divide into two cells: a small polar body cell and a larger mature cell. An ootid is a bigger mature cell.
• The smaller polar body cell, like the others, will eventually disintegrate. Ovulation happens when the oocyte has reached the ootid stage of development. Ovulation causes the follicle to release an ootid. Human egg cells cannot move on their own. Instead, the oocyte is pulled to and into the fallopian tube by finger-like projections.
• The ootid is guided along the fallopian tube by cilia, which are little hair-like projections. If a pregnancy occurs, a sperm cell fertilises the ootid in the fallopian tube. After fertilisation, the ootid develops into an ovum, a fully grown human egg cell. That is correct; the oocyte cannot grow fully without fertilisation.

Post Oocyte formation:

From the oocyte to the ovum to the zygote. During fertilisation, the ovum and sperm cells unite, each with 23 chromosomes. These chromosomes fuse together quickly (albeit not at the exact moment of fertilisation), resulting in a new cell with a complete set of chromosomes. This newly created cell is referred to as a zygote. The zygote will develop into an embryo, and ultimately into a new born baby nine months later.

Conclusion: 

Therefore, in this unit, we study about oogenesis. The process of generating a mature ovum from an oogonia in females is known as oogenesis. It is an ovarian disorder. During oogenesis, a diploid oogonium, also known as an egg mother cell, expands and turns into a diploid main oocyte. This diploid primordial oocyte undergoes the first meiotic division, also known as reductional division, which results in the production of two unequal haploid cells.