Nature, Published online: 21 May 2025; doi:10.1038/d41586-025-01561-7Differences in the pattern of a biochemical modification called DNA methylation in blood-generating cells and their progeny can be used to accurately track clones through differentiation. This approach identified biased expansions of blood stem cells giving rise to myeloid-type cells as a characteristic of ageing in mice and humans. #patterns #dna #modifications #provide #barcode