Extended Data Figure 10.

Signatures of early embryonic mutations.

a, The mutational spectrum for 163 early embryonic mutations is displayed according to the 96 substitution classes (defined by 6 substitution classes (C>A, C>G, C>T, T>A, T>C, T>G) and 16 sequence contexts (immediate 5` and 3` bases to the mutated pyrimidine bases; see Alexandrov et al., Nature (2013) for more details; ref. 7). The observed spectrum can be decomposed into two known mutational signatures (signatures #5 and #1), suggesting endogenous mutational processes are dominantly operative in early human embryogenesis (see Supplementary Discussion 6 for more details).

b, The methylation status of 28 C>T early embryonic mutations occurred at NpCpG sequence contexts. Methylation levels were obtained from Laurent et al., Genome Research (2010). The vast majority of the 28 loci were methylated, which is higher than background (right).