A revolutionary gene-editing technology made headlines this year as much for the ethical and societal issues it raised as for the scientific accomplishments it enabled.
CRISPR (pronounced crisper) burst on the scientific scene in 2012, when researchers transformed what had originally been identified as a rudimentary immune system in bacteria into one of the most powerful tools in molecular biology. Composed of RNA and an enzyme that slices up invading viruses, CRISPR allows researchers to edit nearly any gene in any organism much more precisely and efficiently than older methods.