Gametogenesis:
Introduction: Gametogenesis is the process of gamete formation in the
sexually reproducing animal. The body of every sexually reproducing animal
contains two types of cells. Example: Somatic cell and germinal cell.
Both type of cell have diploid
number of chromosome but each type has its different destiny (function). The
somatic cells form various organs of the body during development growth in a
growing age and maintenance and repair of the body parts. Somatic cells always
divide or multiply by meiotic division. Germinal cell form (Gonads, Testes, and
Ovary) Gametic cell that is sperm and Ova in the animal body. These cells
produce Gametic cell by successive Meiotic and Mitotic division. There are
2-type of Gametogenesis that is Spermatogenesis and Oogenesis.
Spermatogenesis:
The process of formation of male gamete is called ‘’Spermatogenesis’’ It occur in a male gonads, Testes. It is continuous process and various stages of development of sperm occur in a Seminiferous tubule at the some time. Seminiferous tubules are lined by single layer germinal, Epithelial, Which give rise germ cell or gametes. The Germinal Epithelial cell divides Re-divides and produce large number of cells. These are called Spermatogonia / Sperm mother cell.
Phase In
Spermatogenesis:
There are 4 different phases that
is Multiplication, Growth, Maturation, Differentiation / Spermiogenesis.
1. Phase of
Multiplication:
In the phase of multiplication
Epithelia’s cell undergo repeated Meiotic division to form Spermatogonia. These
cell move toward Lumen of Seminiferous tubules and inter into next phase.
2. Phase of
Growth:
In the phase of growth the
cell grows and prepared itself and become in large size called Spermatoside.
They contain sufficient natural material which require for maturation.
3. Phase of
Maturation:
In the 3rd phase each primary Spermatocides
undergo two successive division called 1-Maturation (Reduction) division, in
which the number of chromosome in the nuclei is reduced to half that is haploid
number. In the second Maturation division the secondary Spermatides. There is no change in the haploid number of
Chromosome so this division is simple Mitotic division to form Spermatids.
4. Phase of Differentiation:
In the last differentiation phase the Auto logical change
transform the immobile spermatids into actively mobile sperm is called
‘’Spermiogenesis.’’ As a result of Spermiogenesis active mobile sperm attached
to the Sertoli cell or Supportive cell.
Spermatids:
Metamorphosis of Spermatids into sperm is known as
‘’Spermiogenesis’’ Because sperm is very active mobile cell important for
Fertilization. During Spermiogenesis some change occure in Spermatid.
1. Change In
Nucleus:
Nucleus move toward animal pole
chromatin material become closely pack and looses it entire fluid contain. The
shape of Sperm Nucleus also change that is it becomes elongated and narrow.
2. Aacrosome
Formation:
Acrosome is form by Golgi complex which concentrated near the
anterior end of sperm nucleus to form Acrosome. The Acrosome contain Hydrolytic
enzyme for creating way in the egg wall during fertilization.
3. Change in
Centriole:
Two Centriole move and come to lie
behind the nucleus first is called ‘’Proximal Centriol’ ’and second is Distal ‘’Centriole.’’
It occupies position behind the
proximal. They form axil filament of the flagella.
4. Change in
Mitochondria:
All mitochondria from different parts of spermatid concentration around axil filaments to form middle piece of sperm.
5. Cytoplasmic Change:
Much of cytoplasm is loss and remaining cytoplasm from
condensed layer around the sperm that is it surrounds the middle piece and
posterior part of head.
*Ultra
structure of Mammalian Sperm:
The mature sperm are slender actively motile (mobile) free
swimming. The total length is 56 – 65 Um. The mature sperm contain Head, neck
and tail. The neck is the junction between head and tail.
(1) Head:
Head of sperm is flattened
about 4 – 5 um in length and 13 U in width. The anterior part of head is pear
shaped tapering is called Acrosome. The acrosome contains enzymes which facilitates
penetration of ovum by sperm. It means acrosome play an important role during fertilization.
(2) Neck:
It is short, narrow portion between head
and neck. The proximal centriole is located in the basal end of nucleus to the
axis of tail.
(3) Middle
Piece:
It is about 5 – 9 U in length and 1 U in
width. The mitochondrial helix (spiral) end to end this is the characteristics features
of middle piece. The mitochondria provide energy from sperm movements. The
middle piece is covers with typical structure of flagella.
(4) Principle piece:
It is longer portion of tail having 40-45 U in length
and 0.5 U widths. It laces the mitochondria sheath but it has fibrous sheath
which surround the axil filaments.
(5) End
piece:
It is short, thin cylinder, about 5to 90 length and it
is has typical appearance of flagella.
Significance
of Spermatogenesis:
1. Spermatogenesis it means to maintain
species specific constant chromosome number.
2. As result of Spermatogenesis haploid
(n) sperm are formed because during 1st maturation division half
chromosomes reduce so the 2nd Spermatocytes is haploid cell that is
in them the number of chromosome is reduced to half of the parent cell.
3. As the result of Spermatogenesis, the round and non-motile Spermatid changes into elongated and Motile Sperm which insure fertilization of egg to form diploid zygote which is (2n).
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