Extended Data Fig. 8: Widespread recurrent somatic trisomy 20 across one donor.

a, Scatter plot showing the difference in mean VAF of SNPs on both parental haplotypes of chromosome 20 per sample subjected to panel sequencing versus the Benjamini-Hochberg corrected p-value of a two-sided likelihood ratio test on read count data to test whether both haplotypes are more likely represented by two or one underlying binomial probabilities (Methods). Samples with an absolute VAF difference greater than 0.1 and a corrected p-value lower than 0.1 were deemed to show sufficient evidence of trisomy 20. b, High-level overview of the sampling of fundus, body and antrum in donor PD40293 with respect to other biopsies and the gastric tumour. CI=chronic inflammation, IM=intestinal metaplasia. c, Histology sections of the two histology slides with extensive microdissections of the fundus in PD40293 with annotated microdissected samples and presence of trisomy 20 based on (a). Grey box indicates samples has been whole-genome sequenced rather than subjected to panel sequencing. Scale bar in slide overview images are 1 mm, scale bars in zoomed-in images or 250 µm.