A gene is a length of deoxyribonucleic acid, or DNA, containing instructions for building a specific protein in living organisms. Because the protein products coded for by certain genes are valuable in medicine, industry and other applications, the ability to isolate these genes and make many thousands of copies of them is extremely useful. This process is called gene cloning and has been underway since the latter portion of the 20th century.
Basics of Cloning
A clone, biologically speaking, is an entity that is identical to another entity down to the molecular level—the two entities have the exact same DNA. Clones can exist along the whole structural hierarchy from nucleic acid strands to macromolecules to cells to whole animals. Clearly, the cloning process becomes more elaborate at higher levels of organization; cloning a gene consisting of a DNA segment only a few hundred base pairs long is straightforward, whereas cloning an entire mammal—first accomplished in 1996 when Scottish researchers cloned a sheep, famously named Dolly—is extraordinarily complex.
Creating a Library
In the lab, after a genetic engineer has extracted a sample of an organism's DNA, her next task is to take the sample, which contains copies of all of the organism's genes, and isolate the gene of interest. To do this, she first adds proteins called restriction enzymes to the mix. These enzymes function somewhat like keys in a lock: they recognize specific sequences of DNA and cleave them from the intact strands. The engineer then uses the same restriction enzymes on bacterial DNA to create small circular DNA strands called plasmids, which interact with the cut portions of the organism's DNA to create recombinant DNA.
Once recombinant DNA has been created and a 'library entry' for the particular DNA now exists, the next step is to multiply it. This is done by introducing the plasmid into a bacterium such as Escherichia coli. Every time the bacterial cells divide, which occurs about three times an hour in the case of E. coli, the number of copies of the plasmid doubles. After the desired number of copies of the gene of interest is reached, the engineer breaks apart the bacterial cell wall, 'grabs' the DNA and puts it in human or other cells to initiate cloning in earnest.
Since the advent of gene cloning, the idea of cloning entire human beings has led society at large to be skeptical or even fearful of the technology, given the potential ramifications. As of 2014, however, human cloning was limited to the realm of science fiction. In both 1998 and 2004, researchers in South Korea claimed to have cloned human embryos, but these claims could not be independently verified. Indeed, cloning humans and other primates involves a much higher degree of technical sophistication than do other kinds of gene cloning because of, among other things, the nature of the proteins involved in cell division, in this particular instance.
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