The fears and the hopes of genetically engineering the human race have been haunting the modern mind for the better part of a century, although only in the last decade have techniques been developed that might give us the power to modify the genomes of human beings at the embryonic stage. Foremost among these has been the CRISPR-Cas9 system — a set of bacterial enzymes first identified in the late 1980s, and during just the last few years harnessed as a gene-editing tool. What sets CRISPR apart from earlier genetic modification techniques is its accuracy and versatility: the enzymes that cut the targeted DNA are guided by short sequences of RNA that can be custom-designed for any site in the genome. Earlier genetic engineering methods required different enzymes to target different locations in the genome, but by using RNA instead, CRISPR makes that targeting process much easier. (Although there are some differences in what the terms “genetic engineering,” “genetic modification,” and “gene editing” mean, they are for the most part interchangeable.)
This new gene-editing tool has rapidly become ubiquitous in molecular biology, with many applications beyond gene therapy. For instance, scientists have used CRISPR to remove retroviral sequences from the genomes of pig embryos in the hope of producing pigs with organs that can be transplanted more safely into humans. Because CRISPR is relatively easy to use, some journalists have even speculated that the technique might lead to the democratization of genetic engineering, with “home hobbyists” using it for who-knows-what. This claim seems overblown. While it is true that CRISPR makes the specific task of editing DNA much easier, there are other technically complicated steps and procedures involved in most forms of genetic engineering.
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