How ‘find and replace’ for human DNA works

April 27, 2015

As this Reuters graphic shows, editing DNA using the CRISPR/Cas9 technique works similarly to the “find and replace” function in a word-processing program. First CRISPR — short for “clustered regularly interspaced short palindromic repeats” — searches for a unique string within the DNA sequence. Once found, the Cas9 enzyme cuts the DNA at the prescribed location, and replaces it with healthy DNA.


While the CRISPR/Cas9 technique has been around since 2013, it has never been used on humans, owing to an informal agreement among the world’s scientists. Theoretically, DNA editing could be used to eradicate disease, but changes to DNA are passed down to future generations, an ethical sticking point for some. There are also concerns that people will use the technique for purely cosmetic purposes, or that the wrong gene will be replaced, causing unwanted mutation. At the moment, the scientific community is as interested in defining the ethics of the practice as stopping it permanently.

Meanwhile, science marches on: Last month a Harvard geneticist reported splicing woolly mammoth DNA into lab-grown elephant cells, moving closer to the concept of de-extinction, offering its own ethical conundrum.  

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