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BACK IN THE 1980s, researchers began to notice a strange pattern in the genes of many microbes. There would be a stretch of DNA that read the same forward and backward, then a stretch of what looked like junk, then another palindrome, and so on. No one knew what the segments were for, but they were striking enough that a pair of scientists in Europe dubbed them “clustered regularly interspaced short palindromic repeats,” or Crispr for short.

As it turned out, the mysterious sequences were an immune system. When a microbe was exposed to a new virus, it would cut a swatch of the invader’s DNA (the junk) and store it safely between two dividers (the palindromes). That way, if the virus ever returned, the microbe could simply consult its archive and dispatch the proper immune response.

The task of figuring out the details of that process fell to a later generation of scientists. In 2011, a microbiologist named Emmanuelle Charpentier determined that the Crispr scheme has three key ingredients: an enzyme that acts like a scissors, snipping the strands of the DNA double helix; a guide RNA, which tells the scissors where to cut; and a component that locks the scissors into place. The following year, Charpentier teamed up with biochemist Jennifer Doudna, and the pair asked what proved to be the multibillion-dollar question: Could they exploit this system and use it to edit genes?

The tool they ended up creating—also known, confusingly, as Crispr—not only worked, it effectively blew every existing technology out of the water. To edit a gene using Crispr, all you have to do is give your guide RNA an address corresponding to a particular location on the genome. The scissors will then snip out the selected gene, or even a tiny fragment of the gene, and insert a replacement as needed. (A natural repair mechanism automatically stitches the whole thing back together.)

The result has been transformative. For one thing, Crispr works in almost every animal that scientists have tried, from silkworms to monkeys, and in just about every cell type—kidney cells, heart cells, you name it. (Previous gene-editing techniques even had trouble with rats.) What’s more, Crispr is both fast and cheap. Before Doudna and Charpentier made their discovery, it might have taken more than a year to engineer a mouse with a single mutation. Now it can take as little as two days of work. And while the new editing technique sometimes produces typos, it’s far, far more precise than its predecessors. One scientist told me that with Crispr he needs only 10 cells to yield at least one perfect mutation. In the old days, he would have had to fiddle with about a million cells to get the same result.

More: https://www.wired.com/story/preparing-unleash-crispr-unprepared-world/

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