Q.What is oogenesis? Give a brief account of oogenesis.

Oogenesis is the process of formation of a mature female gamete, the ovum, from the primordial germ cells in the ovary. It begins during embryonic development when millions of gamete mother cells (oogonia) are formed within each fetal ovary through mitotic divisions. These oogonia start dividing and enter meiosis-I but get arrested at the prophase-I stage, now called primary oocytes, which remain surrounded by a layer of granulosa cells forming primary follicles.

At puberty, a few primary follicles mature each cycle. The primary oocyte completes meiosis-I to produce a large secondary oocyte (with most of the cytoplasm) and a tiny first polar body. The secondary oocyte begins meiosis-II but arrests at metaphase-II. Only if fertilization occurs does it complete meiosis-II, releasing a second polar body and forming the mature ovum. The first polar body may also divide, so one oogonium ultimately yields one functional ovum and two or three polar b …

Oogenesis is the biological process through which the female reproductive system produces ova, or egg cells. Unlike continuous sperm production in males, oogenesis in humans begins before birth and resumes only at puberty, with one ovum typically maturing each menstrual cycle. The process unfolds in the ovaries and is intricately tied to a female's reproductive lifespan.

The journey begins during embryonic development. Primordial germ cells in the developing ovary multiply by mitosis to form millions of oogonia. These diploid cells are the starting point. By the time a female foetus is a few months old, the oogonia enter the growth phase and enlarge to become primary oocytes. Crucially, these primary oocytes begin the first meiotic division but then arrest in prophase I—they pause at this stage and remain dormant until puberty. Most of these primary oocytes degenerate over time; only about 60,000–80,000 survive until birth, and far fewer remain by puberty.

At puberty, hormonal signals trigger the resumption of oogenesis. Each month, a few primary oocytes are stimulated to continue development, though typically only one completes the process. The primary oocyte completes meiosis I, but this division is unequal. The cell divides to produce a large secondary oocyte, which receives most of the cytoplasm, and a tiny first polar body that contains very little cytoplasm. This asymmetry ensures that the eventual ovum has sufficient nutrients and cellular machinery to support early embryonic development.

The secondary oocyte then begins meiosis II but arrests again, this time at metaphase II. It is released from the ovary in this state during ovulation. Meiosis II is completed only if fertilisation occurs—when a sperm penetrates the secondary oocyte. This second division is also unequal, producing a large mature ovum (or ootid) and a second polar body. The first polar body may also divide, yielding two more polar bodies. All polar bodies eventually degenerate; they are essentially discarded packets of genetic material, ensuring that only one functional gamete forms from each oogonium. …