Attached to the front of that disk are microscopic tungsten particles 1 micron in diameter coated with thousands of DNA molecules. The particles penetrate the cells and release the DNA, which is diffused into the nucleus and incorporated by the chromosomes of the plant. In all genetic engineering trials, researchers have to be sure the technology has worked. Following the expression of the DNA into the papaya cells by the gene gun, for instance, researchers tested what they hoped were the genetically altered cells to make sure the desired gene transfer had occurred by subjecting the cells to the antibiotic Kanamycin. Only disease resistant cells survive Kanamycin.
Tissue culture is one of the most difficult aspects of genetic engineering and a very delicate task.
At every stage of development, scientists test the tissue for viability and disease resistance by subjecting it to the target disease. At first, they do this in petri dishes, later in the greenhouse, then in field trials, and, finally, on commercial acreage. Clearly, the gene gun and its use has revolutionized genetic engineering in many fields.