Gametogenesis: spermatogenesis vs oogenesisयुग्मकजनन: शुक्राणुजनन व अंडजनन

NCERT Fig 2.8 · Class 12 Biology · Chapter 2 · interactive diagram

Parts and their functions

• Spermatogonium (2n = 46) (शुक्राणुजन) — Multiplies by mitosis from puberty on.
• Primary spermatocyte (2n) (प्राथमिक शुक्राणुकोशिका) — Meiosis I → two secondary spermatocytes.
• Secondary spermatocyte (n = 23) (द्वितीयक शुक्राणुकोशिका) — Meiosis II → two spermatids each.
• Spermatids (n) (शुक्राणुप्रसू) — Four per primary spermatocyte; spermiogenesis turns them into sperms.
• Sperms (n) (शुक्राणु) — Released by spermiation. Process is controlled by GnRH → LH (Leydig cells, androgens) and FSH (Sertoli cells).
• Oogonia (2n) (अंडजनी) — Formed in each fetal ovary during embryonic development; no more oogonia are formed or added after birth.
• Primary oocyte (2n) (प्राथमिक अंडक) — Enters prophase-I of meiosis and gets temporarily ARRESTED there; lies inside a primary follicle.
• Secondary oocyte (n) (द्वितीयक अंडक) — Large haploid cell formed by UNEQUAL meiosis I in the tertiary follicle; released at ovulation.
• First polar body (प्रथम ध्रुवीय पिंड) — Tiny cell from unequal meiosis I — gets very little cytoplasm.
• Ovum (n) (अंडाणु) — Meiosis II of the secondary oocyte is completed only when a sperm enters it.
• Second polar body (द्वितीय ध्रुवीय पिंड) — Formed when meiosis II completes at fertilisation.

Steps

1. Germ cells: spermatogonia (testis) and oogonia (fetal ovary), 2n = 46.
2. They grow into primary spermatocytes / primary oocytes (2n). The primary oocyte is arrested in prophase I.
3. Meiosis I: two equal secondary spermatocytes; but UNEQUAL in the female → large secondary oocyte + first polar body (n = 23).
4. Meiosis II: four spermatids; in the female it completes only at fertilisation → ovum + second polar body.
5. Spermiogenesis: spermatids → sperms, released by spermiation.

Original diagram drawn by Simple Learning Hub, based on NCERT Fig 2.8. Report a mistake