In this article we will discuss about the methods of gene transfer.
Gene transfer can be done by two methods:
(i) Indirect Method through Vectors or Carriers and
(ii) Direct or Vectorless Transfer Method.
The first method includes:
(a) Plasmids and Viruses and
(b) Natural Genetic Engineer,
(a) Plasmids and Viruses:
Recombinant DNA technology involves the transfer of desired genes into vectors such as plasmids or viruses. Cloning of the recombinant DNA (r-DNA) then provides multiple copies.
Natural Genetic Engineer Tumor Inducing (ti) Plasmid:
For example, Agrobacterium tumefaciens is a plant pathogenic bacterium which can transfer part of its plasmid DNA as it infects host plants. Species of Agrobacterium produce crown galls or plant tumors in several dicot plants such as tobacco, tomato, potato, etc.
These bacteria contain large Ti-plasmids (i.e., tumor-inducing plasmids in Agrobactenum tumefaciens) which pass on their tumour causing gene into the genome of the host plant. Thus, galls are formed on the host plant and therefore, these bacteria are known as engineers of plants.
Ti-plasmids can be used as gene vectors for delivering useful foreign genes into target plant cells and tissues. Ti-plasmid vectors can be used for genetic transformation of many important dicot (e.g., potato, tomato, cotton, sunflower, etc.) and monocot (e.g., wheat, rice, etc.) plants.
The vectorless gene transfer includes the following four important methods:
(a) Electroporation:
In which temporary holes produced in plasma membrane of the cell mediate entry of foreign DNA.
(b) Chemical Mediated Gene Transfer:
In which certain chemicals (e.g., polyethylene glycol) help in the uptake of foreign DNA into host cell.
(c) Microinjection:
Introduction of foreign genes into plant or animal cells using micropipettes.
(d) Particle Gun:
In which Tungsten particles coated with foreign DNA are bombarded into target cells.