The BBC reports that researchers, including Craig Ventner of the Human Genome Project, announced that they’ve managed to synthesize a cell’s DNA. This is the “opposite” of mapping DNA: using a genome that’s been mapped, create working DNA and put it in a cell.

According to Ventner, “the new bacteria replicated over a billion times, producing copies that contained and were controlled by the constructed, synthetic DNA.” It’s a big breakthrough — the first step towards custom-engineering life — that could have some dire consequences if not properly regulated.