Two teams have developed innovative new applications of the popular genome-editing method CRISPR. One of the groups has used it to mark and trace cells in a developing animal. In the method’s first test, described online today in Science, the researchers reveal that many tissues and organs in adult zebrafish form from just a few embryonic cells. Other researchers are already looking to adapt the method to mice, or to exploit it to trace the evolution of tumors. The second group found a way to use CRISPR-guided mutations to record a cell’s history for example, the environmental signals that influence it.