Question

Identify the stages of spermatogenesis in sequence from spermatogonia to spermatozoa. How do they differ in the number of chromosomes per cell (haploid/diploid)?

Answer 1

Spermatogenesis:

In testis, the mature male germ cells, spermatogonia produce sperms by the process of spermatogenesis. It occurs in four stages.

• spermatocytogenesis
• Meiosis 1
• Meiosis 2
• Spermiogenesis

Spermatocytogenesis:

The spermatogonia present on the inside wall of the seminiferous tubules multiply by mitotic division and increase in number. Each spermatogonia is diploid containing 46 chromosomes. Some spermatogonia undergo changes they grow, increase the size by accumulating nourishing materials, and are called primary spermatocytes.

Meiosis 1:

A primary spermatocyte is diploid, (2n) with 46 chromosomes (44 + XY). It completes its first meiotic division leading to the formation of two equal, haploid cells called secondary spermatocytes which have only 23 chromosomes (22 + X or 22 + Y).

Meiosis 2:

The secondary spermatocytes undergo the second meiotic division to produce 4 equal, haploid spermatids. The number of chromosomes in each permitted is 23.

Spermiogenesis:

The transformation of spermatid into sperm is called spermiogenesis. The spermatid is non-motile and heavy. It has organelles like mitochondria, Golgi bodies, centrioles, nucleus. During spermiogenesis, the weight of the gamete is reduced along with the development of locomotory structures. A mammalian sperm are flagellated, consisting of four parts namely head, neck, middle piece, and tail.

After spermiogenesis, the sperm heads become embedded in the Sertoli cells and are finally released from the seminiferous tubules by the process of spermiation.

In spermatogenesis, from one primary spermatocyte four haploid sperms are produced.