Biologists continue to hone their tools for deleting, replacing or otherwise editing DNA and a strategy called CRISPR has become one of the most popular ways to do genome engineering. Utilizing a modified bacterial protein and a RNA that guides it to a specific DNA sequence, the CRISPR system provides unprecedented control over genes in many species, including perhaps humans. This control has allowed many new types of experiments, but also raised questions about what CRISPR can enable.

At least one group has already used CRISPR on human embryos, sparking calls for a moratorium on similar work and an international summit at the end of 2015 to discuss the science and ethics of human gene editing. Meanwhile, CRISPR is making it much easier to generate genetically modified animals and plants, creating new regulatory issues that scientists, agencies, politicians, and, ultimately, society must address.

Jon Cohen

Jon is a staff writer for Science.