(A) Barrett’s esophagus occurs at the gastroesophageal junction between esophageal squamous and gastric cardia tissues. Clones within these tissues can be traced using distinctive mtDNA mutations. (B) Conventional scRNA-seq libraries can be enriched for mtDNA mutations, enabling the linking of clones to cell states. (C) UMAPs of scRNA-seq of matching Barrett’s esophagus, esophageal squamous, and gastric cardia tissues for three Barrett’s esophagus patients; tissues contained supporting immune, fibroblast, and vascular cells. Adjacent heatmaps show the allele frequencies (AF) of mtDNA mutations within Barrett’s esophagus, esophageal, and gastric cardia cells. (D) UMAP of scRNA-seq of all the samples collected in this study; highlighted are transitional basal progenitor cells from the normal squamocolumnar junction. (E) Callouts of the transitional cells from (D) featuring the expression of basal progenitor markers. (F) UMAP of scRNA-seq of a single squamocolumnar junction biopsy from patient 9; in the callout is the same UMAP, colored with the allele frequency of mutation 9166T>C. (G) UMAP of scRNA-seq of a single gastric cardia biopsy from patient 9; in the callout is the same UMAP, colored with the allele frequency of mutation 9166T>C.