Knocking out one gene in the snail Lymnaea stagnalis reverses shell coiling. In contrast to the wild-type dextral snail (right), a CRISPR-created snail shows sinistral coiling (left). Disclaimer: AAAS ...

In previous studies, scientists were able to determine an animal's handedness by looking at how the nodal gene was expressed. But Kuroda and her colleagues' results indicate that the decision of which ...