How is it done?

Genetic modifying is the process of adding, deleting or substituting part(s) of an organism’s DNA. To do that, you have to change the organism by “taking parts” (DNA) from other organism(s).

Every genetic engineering experiment includes 3 distinct stages, which are cloning, screening and gene transfer. Here are the stages:

Stage 1: Cloning. A scientist must first get samples of the gene that they want to transfer to another organism. The first step is to get a DNA strand from an organism that has the specified requirements. Using enzymes that cut DNA, they remove the specified gene and let the gene to insert itself into tiny circles of bacterial DNA. The special enzymes cut the DNA and leave sticky ends that attach to similar sticky ends on any other DNA piece cut by the same sort of enzyme. Finally, they let the bacteria carry the gene to infect bacterial cells. They identify the bacterial cells that have succeeded in getting the bacteria and gene. They then grow each of those cells as a “pure cell culture”. Each “culture is a clone” of each other. Each different clone has a different gene.

Stage 2: Screening. They now must select the particular clone which bears the gene that they want. There are many different ways to find a gene; however, one of the most widely used is to test each clone for its ability to stick to a special probe. The probe is fashioned to be made of DNA that will stick to the precise gene you seek and no others. DNA is made of two mirror-image strands (A,T,G,C). A pairs with T and C pairs with G. No other pairs are possible. So, for example, if one sequence is ATTCGGA and then the sequence TAAGCCT will be the only one that pairs with it.

Stage 3: Gene Transfer. Something to keep in mind is that plant cells, unlike animal cells, are encased within a thick cell wall of cellulose. To introduce plant genes, they must find a way to penetrate that thick well. Infection is the easiest way. Infectious bacteria can be used to carry your gene, if the targeted organism will accept the infection. To get the bacteria in, they remove the “wall” and zap the cell with electricity. The shock causes the cell to briefly open the cell’s pores which allows the DNA to slip in. Another way is to, literally, shoot the DNA into the cells with a particle gun.

Afterwards, they select the genes which have the desired characteristics. Using standard tissue culture techniques, they induce these cells to develop into adult genes. At that point the gene engineering experiment is complete.

 From: http://txtwriter.com/onscience/Articles/geneEng.html