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Genome editing can be viewed as a disruptive technology - fundamentally changing how scientists alter genomes. Despite the technique remaining imperfect, there is now a real possibility that we can precisely and accurately change almost any part of any genome, including plants, animals, and human beings. The question is, should we?
Genetic engineering in itself is, of course, not new - various techniques that allow scientists to modify genes have been around for some time. But the difference with genome editing is that it is simple, cheap, and accurate; thereby opening up the potentials of genetic engineering on a hitherto unseen scale.
Genome editing has a broad range of possible applications in areas such as novel medical treatments, vaccine development, crop innovation and environmental remediation. A variety of approaches fit the genome editing moniker, but the emergence of CRISPR-Cas9 has captured the most attention.
What is CRISPR-Cas9?
Editing a genome involves introducing a change to a chosen target within a cell's DNA. The change can take numerous forms, from introducing a small deletion to effecting a precise sequence change.
There are several methods of genome editing, but CRISPR-Cas9 is currently the easiest to set up and use. The CRISPR-Cas9 technique was first published in 2012,2 but is based on a knowledge of short DNA sequences found in simple cells; around since the 1980s. "CRISPR" stands for "clustered regularly interspaced short palindromic repeats".
The technique involves two main steps. First, components of a custom-designed nuclease (called an endonuclease) are introduced to a recipient cell, whereupon they self-assemble. This endonuclease then targets and cuts one or both strands of a chosen DNA sequence. Second, the recipient cell's inherent DNA-repair machinery then repairs the cut and in so doing, introduces the designed change. These changes can comprise anything from a single base pair change to the insertion or deletion of whole genes.3,4
CRISPR-Cas9 is a very flexible system and can be used without expert protein engineering expertise. The nature of the method also means that several changes can be introduced to a cell simultaneously. Scientific publications using this system are rapidly increasing; with over 800 citations in the database PubMed as at November 2015.
However, despite its simplicity and relatively low cost, CRISPR-Cas9 is not perfect. Problems...