First discovered in 1984, retrons are floating ribbons of DNA in some bacteria cells that can be converted into a specific type of DNA—a single chain of DNA bases dubbed ssDNAs (yup, it’s weird). But that’s fantastic news for gene editing, because our cells’ double-stranded DNA sequences become impressionable single chains when they divide. Perfect timing for a retron bait-and-switch.

Normally, our DNA exists in double helices that are tightly wrapped into 23 bundles, called chromosomes. Each chromosome bundle comes in two copies, and when a cell divides, the copies separate to duplicate themselves. During this time, the two copies sometimes swap genes in a process called recombination. This is when retrons can sneak in, inserting their ssDNA progeny into the dividing cell instead. If they carry new tricks—say, allowing a bacteria cell to become resistant against drugs—and successfully insert themselves, then the cell’s progeny will inherit that trait.

Because of the cell’s natural machinery, retrons can infiltrate a genome without cutting it. And they can do it in millions of dividing cells at the same time.