Scientists have tracked the lineages of cancer cells in the past by comparing shared mutations and other variations in their DNA blueprints. These methods...depend to a certain extent on there being enough naturally occurring mutations or other markers to accurately show relationships between cells. ... Instead of simply hoping that a cancer lineage contained enough lineage-specific markers to track, the researchers decided to use Chan’s method to add in markers themselves. “Basically, the idea is to engineer a cell that has a genomic scratchpad of DNA, that then can be ‘written’ on using CRISPR,” Weissman says. This ‘writing’ in the...