GMDNA and natural DNA are indistinguishable according to the most mundane chemistry, i.e., they have the same chemical formula or atomic composition. Apart from that, they are as different as night and day. Natural DNA is made in living organisms; GMDNA is made in the laboratory. Natural DNA has the signature of the species to which it belongs; GMDNA contains bits copied from the DNA of a wide variety of organisms, or simply synthesized in the laboratory. Natural DNA has billions of years of evolution behind it; GMDNA contains genetic material and combinations of genetic material that have never existed.
Furthermore, GMDNA is designed - albeit crudely - to cross species barriers and to jump into genomes. Design features include changes in the genetic code and special ends that enhance recombination, i.e., breaking into genomes and rejoining. GMDNA often contains antibiotic resistance marker genes needed in the process of making GM organisms, but serves no useful function in the GM organism.
The GM process clearly isn't what nature does (see "Puncturing the GM myths", SiS22). It bypasses reproduction, short circuits and greatly accelerates evolution. Natural evolution created new combinations of genetic material at a predominantly slow and steady pace over billions of years.
There is a natural limit, not only to the rate but also to the scope of gene shuffling in evolution. That's because each species comes onto the evolutionary stage in its own space and time, and only those species that overlap in space and time could ever exchange genes at all in nature. With GM, however, there's no limit whatsoever: even DNA from organisms buried and extinct for hundreds of thousands of years could be dug up, copied and recombined with DNA from organisms that exist today.
GM greatly increases the scope and speed of horizontal gene transfer Horizontal gene transfer happens when foreign genetic material jumps into genomes, creating new combinations (recombination) of genes, or new genomes. Horizontal gene transfer and recombination go hand in hand. In nature, that's how, once in a while, new viruses and bacteria that cause disease epidemics are generated, and how antibiotic and drug resistance spread to the disease agents, making infections much more difficult to treat.
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