CRISPR/Cas9 gene editing has made possible a multitude of biomedical experiments including studies that systematically turn off genes in cancer cells to look for ones that the cancer cells heavily depend on to survive and grow. These genes, or ‘cancer dependencies,’ are often promising drug targets. But new research shows that many of these CRISPR screening experiments rely on components, called CRISPR/Cas9 guides, that do not perform equally well in cells from people of all ancestries, which can cause CRISPR screens to miss cancer dependencies.