Let's understand the processes of spermatogenesis and oogenesis step by step. Both are forms of gametogenesis, which is the production of gametes (sperm and eggs) in the testes and ovaries, respectively.

Spermatogenesis (Sperm Formation)

This is the process of producing male gametes (spermatozoa) in the seminiferous tubules of the testes.

Step 1: Multiplication Phase
A diploid spermatogonium (2n) undergoes mitosis to produce more spermatogonia.

Step 2: Growth Phase
Some spermatogonia grow in size to form primary spermatocytes (2n).

Step 3: Maturation Phase (Meiosis)
- Meiosis I: Each primary spermatocyte (2n) undergoes the first meiotic division to form two haploid secondary spermatocytes (n).
- Meiosis II: Each secondary spermatocyte undergoes the second meiotic division to form two haploid spermatids (n). So, one primary spermatocyte produces four spermatids.

Step 4: Spermiogenesis
The non-motile spermatids undergo a process of metamorphosis (spermiogenesis) to become mature, motile spermatozoa (sperm). This involves the development of a tail (flagellum) and the loss of most cytoplasm.

Oogenesis (Egg Formation)

This is the process of producing female gametes (ova) in the ovaries.

Step 1: Multiplication Phase
A diploid oogonium (2n) undergoes mitosis to produce more oogonia. This phase is completed before birth.

Step 2: Growth Phase
Some oogonia grow tremendously in size to form primary oocytes (2n). These primary oocytes get surrounded by layers of granulosa cells to form primary follicles. At birth, a female already has all the primary oocytes she will ever have, arrested in prophase of Meiosis I.

Step 3: Maturation Phase (Meiosis)
- Meiosis I: Just before ovulation, a primary oocyte (2n) completes the first meiotic division. This division is unequal, resulting in one large haploid secondary oocyte (n) and one very small haploid first polar body (n).
- Meiosis II: The secondary oocyte begins the second meiotic division but arrests at metaphase. This division is only completed if fertilization occurs. It is again an unequal division, resulting in one large mature ovum (n) and a second polar body (n). The first polar body may also divide to form two more polar bodies. All polar bodies eventually degenerate.

Key Differences Summary

Location: Spermatogenesis occurs in testes; Oogenesis occurs in ovaries.
Timing: Spermatogenesis is a continuous process after puberty. Oogenesis starts before birth and is completed only after fertilization.
Number of Gametes: One spermatogonium produces four functional sperm. One oogonium produces one functional ovum and polar bodies.
Cytokinesis: Equal in spermatogenesis; Unequal in oogenesis, leading to polar body formation.

Related Topics & Formulae

Related Topics: Meiosis (the cell division that reduces chromosome number by half), Reproductive System anatomy, Hormonal regulation of gametogenesis (e.g., FSH, LH, testosterone, estrogen).

Important Concept (Not a Formula): The ploidy level. The starting cell (spermatogonium/oogonium) is diploid (2n). The final gametes (sperm/ovum) are haploid (n). Meiosis is responsible for this reduction.

Visualization Tip: When drawing the diagrams, focus on the cell size changes. Draw spermatogenesis cells as similar in size. Draw oogenesis with one large cell (oocyte/ovum) and very small polar bodies in each meiotic division.