The gene editors are only getting started

The thing to understand about Crispr isn’t its acronym—for the record, it stands for Clustered Regularly Interspaced Short Palindromic Repeats—but that it makes editing DNA easy, cheap and precise. Scientists have fiddled with genes for decades, but in clumsy ways. They zapped plants with radiation to flip letters of DNA at random, then looked for useful mutations. They hijacked the infection mechanisms of viruses and bacteria to deliver beneficial payloads. They shot cells with “gene guns,” which are pretty much what they sound like. The first one, invented in the 1980s, was an air pistol modified to fire particles coated with genetic material.

Crispr is much more precise, as Ms. Doudna explains in her new book, “A Crack in Creation.” It works like this: An enzyme called Cas9 can be programmed to latch onto any 20-letter sequence of DNA. Once there, the enzyme cuts the double helix, splitting the DNA strand in two. Scientists supply a snippet of genetic material they want to insert, making sure its ends match up with the cut strands. When the cell’s repair mechanism kicks in to fix the cut, it pastes in the new DNA.