Monitoring the errors in the barcode sequence tags and absolute quantitation of target molecules. Results from Ion Proton sequencer data. The target region is TK102U, except in F. (A–D); results obtained using 40 ng of genomic DNA. (A) Distribution of reads per barcode tag. Vertical axis: number of different barcode tags. Horizontal axis: number of reads per tag, given as the common logarithm of the number. (B) Cumulative reads. (C) Proportions of barcode tags by size. (D) Mean proportion of 12-bp barcode tags after including the 11-bp and 13-bp tags that only differed from a 12-bp tag by the insertion or deletion of a single base. The mean proportion represents the average of the proportions of the nearest 11 bins. (E) Estimated number of target molecules after the removal of erroneous tags. Horizontal axis: number of reads used for estimation; the reads were randomly selected from the entire population of reads (‘5 ng’: 1,457,760; ‘10 ng’: 2,251,133; ‘20 ng’: 2,245,038; and ‘40 ng’: 2,395,763 reads). (F) Correlation between the number of molecules and the amount of input DNA after removal of the erroneous tags.