Gene transfer techniques- Plasmids and Balistic

1. Gene transfer techniques 
In the laboratory, specific enzymes may be used to cut and splice DNA:
Restriction enzymes break DNA at specific parts of the molecule (nucleotide base sequences) - usually leaving so called "sticky ends".
This can be done to both DNA from which genes are being taken, and to DNA in which genes are being inserted. Then, DNA ligase enzymes may be used to rejoin such sections into the other DNA.
The DNA containing the selected gene for the desired characteristic may then be inserted into cells of the target organism by means of vectors. There are 2 main types of vectors:plasmids and viruses (see previous notes on micro-organisms).

1.1 Gene transfer using plasmids 
Agrobacterium tumefaciens is a bacterium that contains a section of DNA called a plasmid in addition to its usual component of DNA. This tumour inducing plasmid has the ability to incorporate its DNA into the cells of the plant host, thus acting as a medium to allow the insertion of other genes into crop plants during genetic engineering.

1.2 Gene transfer using viruses
lambda (λ) phage - a bacteriophage which can modify bacteria, stays in the DNA of the host, and replicate the host’s DNA. It does not harm the host during the replication process, but it evolves with the host DNA. The microphage can remain inside the host indefinitely without having any harmful effect. These bacteriophages can be modified using restriction enzymes and foreign DNA. When the bacteriophages are opened, gene modification can be carried out by inserting the desired viral DNA to integrate with the host cells's "chromosome".

2. Others

2.1 Ballistic techniques
Minute tungsten particles are coated with the DNA to be inserted, then shot into the target cells with an explosive charge.

2.2 Electroporation
In this technique, a brief pulse of electric current is passed through the cell, temporarily increasing surface permeability so that DNA is taken up from the surrounding liquid. This has been especially useful with pollen tubes and has resulted in the genetic transformation of seeds.

author: Monica