Biology Today — January 2018

Fig.: Events in spermatogenesis

Each spermatogonium produces four haploid sperms,

having half the number of chromosomes.

Fertilisation of haploid gametes restores the diploid

number of chromosomes in zygote. Thus, spermatogenesis

maintains chromosome number of species.

Crossing over takes place during meiosis I, which brings

about variations.

Signicances of Spermatogenesis

Fig.: Events in spermatogenesis

Spermatogonia

(2n)

Mitosis

Phases in spermatogenesis

Multiplication

phase

Maturation phase

Spermiogenesis

Growth phase

Meiosis I

Meiosis II

Primary

spermatocyte

(2n)

Secondary

spermatocyte

(n)

Spermatozoa

(sperms)

(n)

Spermatids

(n)

Mitosis

Spermiogenesis

The transformation of spermatids into spermatozoa is called spermiogenesis or spermateliosis or differentiation phase.

• The different changes occurring during spermiogenesis are:

(i) Formation of acrosome by Golgi apparatus

(ii) Elongation of nucleus
(iii) Separation of centrioles

(iv) Formation of axial filament from distal centriole

(v) Development of mitochondrial spiral around upper parts of axial filament
(vi) Formation of flagellum

Spermatid

nucleus

Developing

acrosome cap

Developing

acrosome cap Acrosome

cap

Acrosome cap

Nucleus

Nucleus

Head

Midpiece

Tail

(flagellum)

Excess

cytoplasm Mitochondria

Spermatid

nucleus

Mitochondria Mitochondria

Microtubules

Developing

flagellum

Developing

flagellum

Spermatid

nucleus

Sperm

Fig.: Stages in spermiogenesis

• The entire process of spermatogenesis, from primary spermatocytes to mature spermatozoa (sperms) approximately takes
  64 days in man. The normal human male manufactures nearly 200-290 million sperms per day. A very high rate of sperm
  production appears to be necessary to overcome the odds against internal fertilisation.

Spermiation

After their maturation, spermatozoa detach from the Sertoli cells and the process is called spermiation. The released sperms
are stored in epididymis and first portion of vasa deferentia for few weeks. Here, they gain motility. Nutrition is provided by
epithelium of epididymis.

Sperm

These are microscopic and motile cells that remain alive and retain their ability to fertilise an ovum from 24 to 48 hours, after
being released in the female genital tract.