SINCE its discovery in 2012 CRISPR-Cas9, a gene-editing technique, has gone from strength to strength. This tool, developed from a bacterial defence system that cuts up the DNA of invading viruses, permits genetic material to be edited easily and precisely. It has transformed research in biology, and promises to have wide applications in agriculture and medicine.
But it is not ideal. One of its flaws is that its ability to replace genes works best in cells that are replicating, and thus have the correct molecular furniture in place to incorporate the new DNA being delivered. A second is that it starts by breaking the DNA strands so that new material can be inserted into the gap. That can have undesirable effects. A third is that it is not particularly good at correcting point mutations. These are errors which affect only one or two of the bases, known informally as genetic “letters”, in a gene’s DNA sequence. This flaw is especially problematic because tens of thousands…
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