What is spermiogenesis? Demonstrate diagrammatically the process of spermatogenesis.

Spermiogenesis is the final stage of spermatogenesis, in which the maturation of spermatids into mature, motile spermatozoa takes place. The spermatid is a circular cell containing a nucleus, Golgi apparatus, centriole and mitochondria. The process of spermiogenesis is traditionally divided into four stages: the Golgi phase, the cap phase, formation of a tail, and the maturation stage.

Spermatogenesis- The process of formation of male gamete, i.e, spermatozoa. The process of spermatogenesis takes place in the male gonads called testes. Each testis has seminiferous tubules which are lined by cuboidal epithelium called germinal epithelium. The cells of germinal epithelium undergo spermatogenesis to produce sperms. There are Sertoli cells or nurse cells in between germinal cells which provide nourishment to the sperms. Germinal cells in testes are known as primary germinal cells or primordial germ cells.

Primordial cell passes through three phases namely,

1) Multiplication phase

2) Growth phase

3) Maturation phase

Multiplication phase: Primordial cells undergo repeated mitotic divisions to produce a large number of spermatogonia. Each spermatogonium is diploid (2n).

Growth phase: Spermatogonium cell accumulates food and grows in size. Now it is called primary spermatocyte.

Maturation phase: The primary spermatocyte undergoes first meiotic or maturation division. The homologous chromosomes start pairing. Each homologous chromosome splits longitudinally. Chiasma formation results in an exchange of genetic material.

At the end of I meiotic division, two haploid, secondary spermatocytes are formed. Each secondary spermatocyte undergoes II meiotic division and produces spermatids. At the end of maturation phase, each spermatogonium produces four haploid spermatids.

Spermatid is non-motile so it has to undergo spermiogenesis to become functional, motile male gamete, i.e, spermatozoan. Many changes occur in the spermatid like, sperm increases in length, centrioles are distinguished into proximal and distal centrioles, distal centriole gives rise to the axial filament, mitochondria become spirally coiled and Golgi complex forms acrosome.