Gametogenesis Summary
Shared 4/27/2026•2 views
### Spermatogenesis - **Definition:** Process of sperm cell (spermatozoa) formation in males. - **Location:** Seminiferous tubules of the testes. - **Timing:** Begins at puberty and continues throughout life. - **Stages:** 1. **Mitosis:** Spermatogonia (2n) proliferate, forming primary spermatocytes (2n). 2. **Meiosis I:** Primary spermatocytes (2n) undergo meiosis I to form two secondary spermatocytes (n). 3. **Meiosis II:** Each secondary spermatocyte (n) undergoes meiosis II to form two spermatids (n). 4. **Spermiogenesis:** Spermatids (n) differentiate into mature spermatozoa (n) by shedding cytoplasm, forming a head (acrosome, nucleus), midpiece (mitochondria), and tail (flagellum). - **Duration:** Approximately 64-72 days in humans. - **Output:** Four functional spermatozoa from each primary spermatocyte. - **Hormonal Control:** Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH) from the anterior pituitary, and testosterone from Leydig cells. ### Oogenesis - **Definition:** Process of egg cell (ovum) formation in females. - **Location:** Ovaries. - **Timing:** - **Prenatal:** Begins during fetal development (mitosis of oogonia, initiation of meiosis I). Oocytes arrest in Prophase I until puberty. - **Postnatal:** Resumes at puberty. One oocyte typically completes Meiosis I each month, forming a secondary oocyte and first polar body. - **Fertilization:** Meiosis II is completed only upon fertilization, forming an ovum and second polar body. - **Stages:** 1. **Mitosis (Fetal):** Oogonia (2n) proliferate to form primary oocytes (2n). 2. **Meiosis I (Fetal & Puberty):** Primary oocytes (2n) begin meiosis I, arresting in Prophase I. At puberty, one primary oocyte per month completes Meiosis I, forming a large secondary oocyte (n) and a small first polar body (n). 3. **Meiosis II (Fertilization):** Secondary oocyte (n) arrests in Metaphase II. If fertilized, it completes Meiosis II, forming a large ovum (n) and a small second polar body (n). - **Duration:** Can take decades, from fetal life to menopause. - **Output:** One functional ovum and two or three non-functional polar bodies from each primary oocyte. - **Hormonal Control:** FSH and LH from the anterior pituitary, and estrogen and progesterone from the ovaries. ### Comparison: Spermatogenesis vs. Oogenesis | Feature | Spermatogenesis | Oogenesis | | :-------------- | :-------------------------------------------- | :-------------------------------------------- | | **Location** | Testes (seminiferous tubules) | Ovaries | | **Timing** | Continuous from puberty to old age | Discontinuous; prenatal start, pauses, ends at fertilization/menopause | | **Output** | 4 functional sperm per primary spermatocyte | 1 functional ovum per primary oocyte | | **Cell Size** | Equal cytoplasmic division | Unequal cytoplasmic division | | **Polar Bodies**| None | 2-3 non-functional polar bodies | | **Meiosis I** | Completed continuously | Arrested in Prophase I until puberty | | **Meiosis II** | Completed continuously | Arrested in Metaphase II until fertilization | | **Gamete** | Small, motile (spermatozoon) | Large, non-motile (ovum) |
