Question

Explain oogenesis in detail.

Answer 1

Oogenesis is the formation of the female gamete in the ovary. It begins before birth, pauses during development, and resumes after puberty.

1. Multiplication: Oogonia multiply by mitosis in the foetal ovary. They are diploid.
2. Growth: Some oogonia enlarge and become primary oocytes. These begin meiosis I and remain arrested in prophase I until puberty.
3. Maturation: During a reproductive cycle, a selected primary oocyte completes meiosis I, producing a large secondary oocyte and a small first polar body by unequal division.
4. The secondary oocyte begins meiosis II and is ovulated while arrested at metaphase II. If a sperm enters, meiosis II is completed, producing the ovum and a second polar body.
5. The polar bodies usually degenerate. The large ovum retains most of the cytoplasm and nutrients.

Thus, one primary oocyte produces one functional ovum. The ovulated cell is a secondary oocyte; it completes meiosis II only after sperm entry.