Fig. 1: Schematic illustration of molecular barcoding systems.

a Example of a simplified ligation-based barcoding system. UIDs attached by ligation ensure the original molecules’ identity in this system. b When incorporating UIDs via PCR primers, UIDs are overwritten during repeated PCR cycles. c Creating a linkage between the two strands using the shared UID. The small red block in the sequence indicates a nucleotide variant, and the small yellow block in the sequence indicates a polymerase or sequencing error introduced during the preparation steps. UID unique identifier, CID, cluster identifier.