Extended Data Figure 3 |. Contexts of single-base substitutions corroborate the quality of somatic mutation calls.

| a, The proportion of somatic mutations identified in chronically sun-exposed, intermittently sun-exposed, and sun-shielded skin that belong to each of the 96 trinucleotide substitution contexts. Note the similarity to signature 7 (shown for reference in panel c), albeit to a lesser extent in sun-shielded skin cells. b, Tri-nucleotide contexts of variants from sun-exposed skin validated to be somatic mutations by RNA-seq or phasing as well as variants inferred to be somatic mutations by their variant allele frequency (VAF). Note the similarity to signature 7. The tri-nucleotide contexts of remaining variants (assumed to be amplification artifacts) are also shown. c, Predefined mutation signatures shown for reference; Signature 7 (associated with UV-radiation-induced DNA damage)⁵¹, and SBS scE and SBS scF, which are associated with single-cell whole genome amplification artifacts¹⁸.