CRISPR-based techniques allow the reconstruction of the “family tree” of the cells that compose an animal’s body by marking them with a pattern of deletions and insertions. This kind of barcoding has already helped trace embryo growth and organoid development and is shedding light on essential oncology questions by catching cancer in the act. Read how “Single-cell lineages reveal the rates, routes, and drivers of metastasis in cancer xenografts” in this Science paper and the news from Whitehead Institute.