3. How is this done?

There are a number of techniques in the genetic engineer's toolkit. Biochemical 'scissors' called restriction enzymes are used to cut the strings of DNA in different places and select the required genes. These genes are usually then inserted into circular pieces of DNA (plasmids) found in bacteria. Because the bacteria reproduce rapidly, within a short time thousands of identical copies (clones) can be made of the 'new' gene. Two principal methods can then be used to insert a 'new' gene into the DNA of a plant that is to be engineered.

1.    A 'ferry' is made with a piece of genetic material taken from a virus or a bacterium. This is used to infect the plant and in doing so smuggle the 'new' gene into the plant's own DNA. A bacterium called Agrobacterium tumifaciens which usually causes gall formation in plants is commonly used for this purpose.

Or

2.    The genes are coated onto large numbers of tiny pellets made of gold or tungsten, which are fired with a special gun into a layer of cells taken from the recipient plant. Some of these pellets may pass through the nucleus of a cell and deposit their package of genes, which in certain cases may be integrated into the cell's own DNA.

Genetically engineered (GE) animals and fish are produced by microinjection. Fertilised eggs are injected with new genes which will, in some cases, enter the chromosomes and be incorporated into the animal's own DNA.

Because the techniques used to transfer genes have a low success rate, the scientists need to be able to find out which of the cells have taken up the new DNA. So, before the gene is transferred, a 'marker gene' is attached which codes for resistance to an antibiotic. Plant cells which have been engineered are then grown in a medium containing this antibiotic, and the only ones able to survive are those which have taken up the the 'new' genes with the antibiotic-resistant marker attached. These cells are then cultured and grown into mature plants.

It is not possible to guide the insertion of a new gene with any accuracy, and this random insertion may disrupt the tightly controlled network of DNA in an organism.

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