he three very effective modes of gene transfer
Transformation, Transduction and Transfection
observed in bacteria fascinated the scientist
leading to the development of molecular cloning.
The basic principle applied in molecular cloning
is transfer of desired gene from donor to
a selected recipient for various applications
in the field of medicine, research, gene therapy
with an ultimate aim of beneficial to the
mankind.
Transformation: Transformation is the naturally
occurring process of gene transfer which involves
absorption of the genetic material by a cell
through cell membrane causing the fusion of
the foreign DNA with the native DNA resulting
in the genetic expression of the received
DNA.
Transformation is usually a natural method
of gene transfer but as a result of technological
advancement originated the artificial or induced
transformation.
Thus there are two types called as natural
transformation and artificial or induced transformation.
In natural transformation, the foreign DNA
attaches itself to the host cell DNA receptor
and with the help of the protein DNA translocase
it enters the host cell.
The presence of nucleases restricts the entry
of two strands of the DNA, destroys a single
strand thus allowing only one strand to enter
the host cell.
This single stranded DNA mingles with the
host genetic material successfully.
The artificial or induced method of transformation
is done under laboratory condition which is
either a chemical mediated gene transfer or
done by electroporation.
In the chemical mediated gene transfer, the
cold conditioned cells in calcium chloride
solution are exposed to sudden heat which
increases the permeability of the 
cell membrane allowing the foreign DNA.
The electroporation method as the name indicates,
pores are made in the cell by exposing it
to suitable electric field, allowing the entry
of the DNA.
The opened up portions of the cell are sealed
by the ability of the cell to repair.
Transfection: One of the methods of gene transfer
where the genetic material is deliberately
introduced into the animal cell in view of
studying various functions of proteins and
the gene.
This mode of gene transfer involves creation
of pores on 
the cell membrane enabling the cell to receive
the foreign genetic material.
The significance of creating pores and introducing
the DNA into the host mammalian cell contributed
to different methods in transfection.
Chemical mediated transfection involves use
of either calcium phosphate or cationic polymers
or liposomes.
Electroporation, sonoporation, impalefection,
optical transfection, hydro dynamic delivery
are some of 
the non chemical based gene transfer.
Particle based transfection uses 
gene gun technique 
where 
a nanoparticle is used to transfer the DNA
to host cell or by another method called as
magnetofection.
Nucleofection and use of heat shock are 
the other evolved methods for successful transfection.
