How NGS Works

The role of an NGS device is to distill a specially prepared library of DNA molecules into a long text file of sequences, one line for each sequenced molecule. NGS sequencers perform this molecule-to-text mapping across many research and clinical contexts, spanning everything from RNA sequencing in broccoli[11] to ribosome profiling in bacteria [12] to DNA sequencing for NIPT in pregnant women[13]. These applications of NGS are distinguished primarily by the steps upstream of DNA being injected into the sequencer, termed “library preparation.” Mirroring the diversity of upstream sample preparation methods is a comparably vast range of downstream analyses, one of which is the analysis method for NIPT, covered in detail in Chapter 3. In addition to describing how an NGS machine sequences DNA, this section discusses NIPT-specific workflows upstream and downstream of sequencing.