DNAsequencing

DNA sequencing is the process of determining the precise order of nucleotides within a DNA molecule. The sequence of bases—adenine, cytosine, guanine, and thymine—encodes genetic information used by living organisms and many viruses.

Early methods, such as Sanger sequencing introduced in 1977, used labeled nucleotides and chain termination to read short fragments. The method was the standard until the first high-throughput sequencing technologies emerged in the mid-2000s, enabling massively parallel sequencing of millions of fragments and vastly reducing cost and time. Modern sequencing can be grouped into short-read platforms, which generate many short fragments that are computationally assembled, and long-read platforms, which read longer stretches of DNA directly. Third-generation technologies, including single-molecule real-time and nanopore sequencing, provide longer reads and can sequence native DNA without amplification in some cases.

Applications include whole-genome sequencing, exome sequencing, targeted gene panels, and metagenomics. In medicine, sequencing supports diagnosis of genetic disorders, cancer genomics, pharmacogenomics, and infectious disease surveillance. In research and agriculture, it is used for evolutionary studies, gene discovery, and crop improvement.

Sequencing data require computational analysis for base-calling, alignment to reference genomes, assembly, and variant detection. Accuracy depends on chemistry, sequencing depth, and bioinformatic processing. The cost per genome has fallen dramatically since the 2000s, expanding use but also raising concerns about privacy, data ownership, and ethical considerations. Limitations include difficulty sequencing highly repetitive regions, interpreting structural variation, and the need for validated interpretation frameworks.