Introduction:-
As we studying the development of human; there are two familiar words you may have come across about it as growth and development in your former studies.
Lets an example ;two persons named as ‘A’ and ‘B’ are in same age group(5years) but ‘A’ is taller than ‘B’;here we can not expect more or high (I.Q) level in case of A than B;it is simply the result of growth and both have approximately same brain development,there is another side of observation can be obtained that the ‘B’ may be more I.Q than ‘A’ as a result of proper development of brain in ‘B’.So we can not link growth and development as one thing but can be studies as parallel phenomena .
‘Developmental Biology’ moreover combine the two process which play a vital role in development of an oraganism.Growth is restricted to certain time or age whereas development is a lifelong process.
History of Developmental Biology:-
Therefore Aristotle was the first embryologist who carried out the experiment and noted down the experience in 3 weeks incubation periods of birds (Scott F.Gilbert, Developmental Biology,second edition) but still the development process was a puzzle behind the knowledge of developmental biology.
Everyone wondering to acquire the knowledge about the developmental process of multicellular organism though it is a slow and steady process leading to the complexity .
As every multicellular organism developed from a single celled zygote then result the embryo by equational division of zygote in 2,4,6,8… and so on manner;and this phenomenon are under the embryological perspective,but by considering the embryology the knowledge will be confined to that extent as gamete formation and till the formation of foetus (en.m.wikipedia.org). Therefore the concept came as developmental biology ; the development process is not confined or restricted to birth rather continues till death.Because day by day old cell degenerate and new cell develop and carried out the cellular activities for smoother continuation of life,like blood cell formation; cell of epidermis too regenerate when old cell worn-out .It was very known by Karl Ernst Von Baer ‘Father of modern embryology’.
Phases of Development:-
- Gametogenesis: Gametogenesis is the process of formation of gamete i.e sperm and ovum in male and female respectively.
- Fertilization: Fertilization is the phenomena of fusion of ovum and sperm to form zygote.It is a single diploid cell,during fertilization only nucleus will enter into the ovum.
- Cleavage: The first and foremost role of zygote is dividing as a result of which lots of new cells form,so increase in cell number take place.
- Blastulation: During blastulation,the mass of cells form a hollow ball.
- Differentiation: In the process of differentiation cell get differentiated and forms the cavities,the inner cell layer is called inner cell mass and outside cell layer is called trophoblast.The inner cell mass developed into three germ layer and outer trophoblast forms placenta.The 3 germ layer are ectoderm, endoderm and mesoderm which forms the respective tissues.
- Organogenesis: The formation of different vital organ along with the essential organ from the different germinal layers.Ectoderm produce its own nature of organ which is different from endoderm and mesoderm and vice-versa.Different predetermined organs are produce from different germ layers.
- Metamorphosis: It is generally found in lower grade animals.Mostly found in invertebrates.Due to make the animal more efficient to adapt with environment,metamorphosis occurs.Metamorphosis is the process of formation of adult organism from sexually and physiologically immature organism.
Differentiation and Growth:-
First of all by taking the process of differentiation into consideration;we can explain it as a process of diversification of single cell into numerous cell types.A single celled zygote can divides and then form numerous cells like neurons,muscle cells,bone cells,blood cells etc in the process bof differentiation and this follows a complex phenomena to produce such cells.Genetic factor play a vital role in differentiation process.
Differential gene expression:-
Cell-Cell Interaction:-
- The reciprocal induction is direct opposite to inductive interaction where the responder act as inducer and inducing tissue act as respondent
- In instructive interaction certain cells are couldn’t show their behaviour without the signal of inducing cells and does not differentiate .
- The third type of interaction is permissive i.e some cell contain all the potentiality to express but required the condition or permission to express in thier own way.
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