<P> There are a number of techniques available for inserting the gene into the host genome . Some bacteria can naturally take up foreign DNA . This ability can be induced in other bacteria via stress (e.g. thermal or electric shock), which increases the cell membrane's permeability to DNA; up - taken DNA can either integrate with the genome or exist as extrachromosomal DNA . DNA is generally inserted into animal cells using microinjection, where it can be injected through the cell's nuclear envelope directly into the nucleus, or through the use of viral vectors . </P> <P> In plants the DNA is often inserted using Agrobacterium - mediated recombination, taking advantage of the Agrobacteriums T - DNA sequence that allows natural insertion of genetic material into plant cells . Other methods include biolistics, where particles of gold or tungsten are coated with DNA and then shot into young plant cells, and electroporation, which involves using an electric shock to make the cell membrane permeable to plasmid DNA . Due to the damage caused to the cells and DNA the transformation efficiency of biolistics and electroporation is lower than agrobacterial transformation and microinjection . </P> <P> As only a single cell is transformed with genetic material, the organism must be regenerated from that single cell . In plants this is accomplished through the use of tissue c ulture . In animals it is necessary to ensure that the inserted DNA is present in the embryonic stem cells . Bacteria consist of a single cell and reproduce clonally so regeneration is not necessary . Selectable markers are used to easily differentiate transformed from untransformed cells . These markers are usually present in the transgenic organism, although a number of strategies have been developed that can remove the selectable marker from the mature transgenic plant . </P> <P> Further testing using PCR, Southern hybridization, and DNA sequencing is conducted to confirm that an organism contains the new gene . These tests can also confirm the chromosomal location and copy number of the inserted gene . The presence of the gene does not guarantee it will be expressed at appropriate levels in the target tissue so methods that look for and measure the gene products (RNA and protein) are also used . These include northern hybridisation, quantitative RT - PCR, Western blot, immunofluorescence, ELISA and phenotypic analysis . </P>

Describe genetic engineering and give one example of it