Rucete ✏ Biology In a Nutshell
1. Oogenesis (Egg Formation)
- Begins during fetal development
- Oogonia (2n) divide by mitosis to produce primary oocytes (2n)
- Primary oocytes enter Meiosis I, but pause in prophase I until puberty
- Each month after puberty:
- One primary oocyte completes Meiosis I → forms secondary oocyte (n) and a polar body (n)
- The secondary oocyte begins Meiosis II but pauses in metaphase II
- Meiosis II is only completed if fertilization occurs
- Result: one functional ovum (n) and three polar bodies (which disintegrate)
2. Ovulation
- The process where the secondary oocyte is released from the ovarian follicle
- If sperm is present, fertilization may occur in the fallopian tube
3. Spermatogenesis (Sperm Formation)
- Begins at puberty in the seminiferous tubules of the testes
- Spermatogonia (2n) divide by mitosis to form primary spermatocytes (2n)
- Primary spermatocytes undergo Meiosis I → two secondary spermatocytes (n)
- Secondary spermatocytes undergo Meiosis II → four spermatids (n)
- Spermatids mature into sperm cells (spermatozoa) with the help of Sertoli cells
Tags:
Biology in a nutshell