With the discovery of the double helix, we learned how genes are copied and how genetic information was passed on. From there, Francis Crick, Marhsall Nirenberg and Jacques Monod, cracked the genetic code and discovered how genes perform other vital tasks besides copying themselves. Unlocking this code brought about Hermann Muller’s realization that there could be a possibility to introduce mutations, allowing humanity to direct evolution in desirable ways. But how could engineers do this? The first process of “cutting and pasting enzymes”, was described by Swiss microbiologist Werner Arber, in the 1950s. Arber noted that if such enzymes “target specific stretches of DNA”, they could be used to “cleave it into fragments at specific spots”. Which is exactly what American microbiologist Hamilton Smith did with a restriction enzyme. Today there are more than 3,000 restriction enzymes known, each specialized to a particular DNA sequence. These enzymes allow scientists to splice both whole and part of genes.
So what happens with these restriction enzymes once they’ve been “cut”? Once cleaved, enzymes called ligases are used to stick them back together. These ligases can join genomes of another organism together, creating what is known as recombinant DNA. These pieced together sequences are created in the lab and was first done by biochemist Paul Berg in the 1970s. Berg placed together parts of a monkey virus called SV40 and a bacteriophage. He wanted to take this modified virus and place it into E. coli bacteria to allow it to replicate, but something caused him to pause. SV40 was known to promote tumor growth in mice, and E. coli was found in the human gut, if the recombinant virus were to get out, people could be infected and a potential biohazard could play out with people churning out toxic SV40 proteins. With this threat a possibility Berg held off on his experiments until 1976 after safety protocols had been drawn up at the Asilomar conference. Still to this day, even with such safety precautions in place, many still argue that more precautions should be considered.
Nonetheless, Herbert Boyer and Stanley Cohen, possibly being a bit reckless, became the first scientists to successfully create the first “true” genetically modified organisms. The two added a gene that confers antibiotic resistance to a plasmid, and inserted it into E. coli turning the bacteria antibiotic-resistant. After completing this, Boyer saw potential in the medical field for this type of experimentation. If human genes were engineered into plasmids, it would be possible to manipulate bacteria to make proteins that could be used in therapy. Boyer took his idea and ran with it, setting up Genentech and commercializing the technology, with their first successful recombinant version of insulin.
Today similar approaches are used to create scores of drugs and other commercial products. Many of which have advantages over the alternatives. For example, the human growth hormone used to treat dwarfism, once extracted from the pituitary glands of cadavers, which had the possibility of infecting recipients with the human equivalent of mad cow disease. Thanks to all of these trailblazing men the recombinant version we now have poses no such risk.
Reference: Henderson, Mark, Joanne Baker, and A. J. Crilly. "Chapter 8 - Genetic Engineering." 100 Most Important Science Ideas: Key Concepts in Genetics, Physics and Mathematics.