FUNDAMENTAL CHARACTERS OF EMBRYONIC DEVELOPMENT
1. GAMETOGENESIS-
Testes & ovaries are collectively called as gonads. Similarly sperms & ova are collectively called as gametes. The formation of gametes in the gonads is called as gametogenesis.
Gametogenesis is of 2 types -
(a) Spermatogenesis - formation of haploid sperms in the testes.
(b) Oogenesis - formation of haploid ova in the ovaries.
2. FERTILIZATION
Fusion of haploid ova & sperms to form diploid zygote is called as fertilization. The sperm activates the ovum to develop.
3. CLEAVAGE
It is a sequence of mitotic divisions which results in the formation of multicellular morula. The resulting cells are called as blastomere.
Cleavage is a type of mitotic division, resulting unicellular zygote convert into multicellular structure.
Formation of blastula through zygote, this process is called blastulation.
4. GASTRULATION
The cells of blastula exhibits morphogenetic movements to form a triploblastic structure called gastrula. The process is called as gastrulation.
The blastocoel is lost gradually and a gastrocoel is formed.
The three germ layers formed in gastrula are ectoderm, mesoderm & endoderm.
A cavity present in the gastrula is called as Archenteron.
5. ORGANOGENESIS
The germ layers form various organs, Firstly, they form small groups of cells which are called as primary organ rudiments.
The primary organ rudinents form secondary organ rudimetns which finally form tissues & organs in adults.
6. GROWTH
The tissue & organs after formation exhibit grwoth & increase in volume.
The growth is due to constant mitosis and sythesis of nuclear & cytoplasmic materials. Gradually, the embryo grows & take the parental shape.
7. DIFFERENTIATION
The growth of embryo is accompanied with differentiation which is of three types -
(a) Histological differentiation
(b) Chemical differentiation
(c) Physiological differentiation
8. METAMORPHOSIS