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.