Sequence read processing Demultiplexing NGS sequence runs are often performed with multiple samples pooled together. In such cases, an index tag (or "barcode") - a unique sequence of between 6 and 12bp - is ligated to each sample's genetic material so that the sequence reads from different samples can be identified. The process of demultiplexing (dividing sequence reads into separate files for each index tag/sample) may be performed automatically by the sequencing hardware. Alternatively the reads may be lumped together in one file with barcodes still attached, requiring you to do the splitting using software. In such cases, a "mapping" file is used which indicates which barcodes correspond to which samples. Sequence demultiplexing 1.24 Assigning sequence reads to separate groups / files based on their index tag (sample origin).