Embryology : CBCS zoology 6th semester
Gametogenesis
- What is gametogenesis?
Definition: It is the formation of a haploid gametes
from diploid germ cells in the gonads ( Testes or Ovary ) for sexual
reproduction.
It has two types. 1) Spermatogenesis 2) Oognesis
- What is fertilization?
Fertilization:
Sperm (n) + Egg/Ova (n) = Zygote (2n)
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| Fig: Formation Of Zygote to fused male & Female Gamete |
Fertilization
is a process, in which mature male gamete (sperm) & mature female gamete (Ova/egg) fused
at fallopian tube of female reproductive organ and formed a 2n number of zygote
. Mature human sperm has 23 numbers of chromosomes & Mature human egg has
only 23 numbers of chromosomes. During fertilization the chromosomes form the
sperm & eggs unit to give the fertilized egg ( Which is called Zygote )
& it has 46 nnumbers of chromosomes.
After that
mitotic cell divisions are occure at uterus ade formed Morula . This
mitotic cell division is called Cleavage. Morula has 16 to 32 numbers of
cells & that cells are divide as outer cell and inner cell.
During the process of blustulation morula turned into Blastula. It has a blastoceal. And it form Gastrula through the process of gastrulation. During Organogenesis / Differentiation / Specialization three types of cells – 1) Outer Ectoderm
2) Middle Mesoderm and
3) Inner Endoderm are formed.
| • Outer Ectoderm form skin, Sense organ & Nervous system. • Middle Mesoderm form Muscle, skeleton Inner Endoderm form Digestive system, Reproductive system & Respiratory system of the offspring. |
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- What is spermatogenesis?
Defination- It is the formation of haploid sperm in the
seminiferous tubules of Male gonads (Testes)
Formation of Spermatid: It is developed from a single cell called Primordial
germ cell. It has three stages –
1) Multiplication Phase
2) Growth Phase
3) Maturation Phase
1)
Multiplication Phase: At Seminiferous tubules Primordeal germ cell enters 1st
Mitotic Cell division and form Spermatogonia or Sperm Mother Cell. Mitotic cell
division is a multiple process, it’s why every cell ( Primary germ cell ) form
4 Spermatogonia.
Every
spermatogonia growth through Accumulation of cytoplasm and Replication of DNA.
This cell is known as Primary spermatocyte.Every Primary spermatocytes enters
into the 1st meiosis division and formed two secondary spermatocyte.
Again this secondary spermatocytes formed two spermatid through 2nd
Meiosis division. Now this spermatid form mature sperm. Ultimately every
spermatogonia form four spermatid and it form sperm.
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| fig: Spermatogenesis from Primordial Germ cells |