Scientists made several crucial advances this year in rewriting the genetic code using CRISPR/Cas9 — a tool made of protein and RNA that can be customized to efficiently edit DNA.

For years, hype has been building around CRISPR/Cas9’s tremendous potential — to permanently cure genetic diseases like cystic fibrosis and help the body fight infections, as well as create better biofuels and more resilient crops. The technology works by borrowing a system bacteria use to fight viruses and programming it to snip targeted sections of the genome and swap in a replacement.

But a big hurdle was the concern that getting an edit wrong could create a problem that doesn’t just harm an individual organism but ripples through generations of progeny. In October, researchers at Harvard University and MIT presented two approaches to get around this.