next-generation sequencing

Next-generation sequencing is what made reading genomes fast and affordable. Where the older Sanger method reads fragments one at a time, NGS reads millions of fragments side by side in a single run — like photographing a whole stadium crowd at once instead of interviewing each person separately.

The DNA is chopped into many short pieces, each piece is attached to a surface and copied into a tiny cluster, and the instrument then reads all the clusters simultaneously, recording one base of each fragment in every cycle. Because so many reactions happen in parallel, the cost per base dropped dramatically and a human genome that once took years can now be sequenced in a day.

The trade-off is read length and bookkeeping. Most NGS reads are short — often a few hundred bases — so reassembling them across long, repetitive regions can be hard, and the flood of data demands serious computing. These short-read platforms now dominate research and clinical genomics, increasingly complemented by long-read technologies that span the regions short reads struggle with.