Question

What is oogenesis? Describe the process of oogenesis with diagram.

Hint:

Trace the path: oogonium, primary oocyte (arrested at prophase I), secondary oocyte plus polar body, ovum plus polar body (after fertilisation).

Answer 1

Understanding the Question:
Oogenesis is the process by which a female's primary germ cells develop into a mature, fertilisable ovum (egg) inside the ovary.

Detailed Explanation:
It begins in the foetal stage itself, when oogonia (diploid germ cells) in the ovary multiply by mitosis and then enter meiosis, but this meiosis pauses at prophase I, so the cell is now called a primary oocyte.
Millions of primary oocytes stay arrested in this state, each surrounded by a layer of granulosa cells forming a primordial follicle, until puberty begins.
From puberty onward, in each menstrual cycle a few follicles start to grow under hormonal stimulation (FSH), and usually one primary oocyte completes its first meiotic division.
This first division is unequal, giving a large secondary oocyte and a tiny first polar body, so nearly all the cytoplasm and nutrients stay with the future egg.
The secondary oocyte begins the second meiotic division but again arrests, this time at metaphase II, and it is released from the ovary in this state during ovulation.
Meiosis II is completed only if a sperm fertilises the secondary oocyte, producing the mature ovum plus a second polar body, while an unfertilised oocyte simply degenerates.
Diagram (described): Oogonium (2n) leads by mitosis to more oogonia, one of which enlarges into a Primary Oocyte (2n, arrested at prophase I inside a primordial follicle) leads by meiosis I to Secondary Oocyte (n) plus first Polar Body (n) leads by meiosis II, completed only after fertilisation, to Ovum (n) plus second Polar Body.

Final Answer:
Oogenesis converts a diploid oogonium into a haploid ovum through two unequal meiotic divisions, with the second division completing only after fertilisation, producing one functional egg and up to three polar bodies.