Which among the following is the correct sequence of stages in spermatogenesis?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Spermatogonia - primary spermatocyte - secondary spermatocyte - spermatid - sperm
Spermatogenesis starts at puberty in the seminiferous tubules. Spermatogonia (diploid) multiply by mitosis. Some become primary spermatocytes, which complete meiosis I to give two haploid secondary spermatocytes. These complete meiosis II to give four spermatids, which change into sperms by spermiogenesis.
Option (1) Spermatid - primary spermatocyte - spermatogonia - sperm — Incorrect. It starts with the spermatid, which is a late stage, and places spermatogonia after the spermatocyte. The order is reversed.
Option (2) Spermatogonia - primary spermatocyte - secondary spermatocyte - spermatid - sperm — Correct. Spermatogonia → primary spermatocyte → secondary spermatocyte → spermatid → sperm follows the order of the divisions: mitosis, meiosis I, meiosis II and then spermiogenesis.
Option (3) Primary spermatocyte - spermatogonia - secondary spermatocyte - spermatid - sperm — Incorrect. The primary spermatocyte is formed from spermatogonia, so it cannot come before them.
Option (4) Spermatogonia - secondary spermatocyte - primary spermatocyte - spermatid - sperm — Incorrect. The secondary spermatocyte is formed by meiosis I of the primary spermatocyte, so it cannot come before it.
NCERT Extract:
Gametogenesis – “… The spermatogonia (sing. spermatogonium) present on the inside wall of seminiferous tubules multiply by mitotic division and increase in numbers. Each spermatogonium is diploid and contains 46 chromosomes. Some of the spermatogonia called primary spermatocytes periodically undergo meiosis. A primary spermatocyte completes the first meiotic division (reduction division) leading to formation of two equal, haploid cells called secondary spermatocytes, which have only 23 chromosomes each. The secondary spermatocytes undergo the second meiotic division to produce four equal, haploid spermatids (Figure 2.5). … The spermatids are transformed into spermatozoa (sperms) by the process called spermiogenesis.”
Figure 2.5 Diagrammatic sectional view of a seminiferous tubule (enlarged)