DNA sequencing

DNA sequencing is the act of reading the order of letters in a piece of DNA — figuring out, base by base, whether each position is an A, C, G, or T. It is the fundamental tool that turns an invisible molecule into text a scientist can study.

Several different chemistries can accomplish this. The classic Sanger method reads one fragment at a time with high accuracy, while next-generation methods read millions of fragments at once. Newer long-read technologies can sequence very long stretches in a single pass. They all share the same goal: recover the exact sequence of bases.

Sequencing can target a single short region, an individual gene, all the protein-coding parts, or an entire genome. The choice of technology depends on how long, how accurate, and how cheap the read needs to be. No method is perfect — every sequencer makes some errors, so important results are usually confirmed by reading the same region multiple times.