What Is DNA Sequencing?

DNA sequencing is the determination of the precise order of nucleotide bases, adenine (A), cytosine (C), guanine (G), and thymine (T), along a strand of deoxyribonucleic acid. The resulting base sequence, read as a linear string, encodes biological information ranging from individual genes to entire genomes. Sequencing technology has driven successive revolutions in genetics, medicine, and biotechnology since the 1970s, and the computational methods needed to assemble, align, and interpret sequence data have made it a field of active interest for electrical engineers, computer scientists, and signal processing researchers alongside biologists.

The applications of sequencing span basic research and clinical medicine. Identifying disease-causing mutations, tracking pathogen evolution, profiling cancer genomes, and characterizing human genetic variation all depend on the ability to read DNA accurately and at scale. Reductions in cost, from roughly 100 million dollars per genome in 2001 to a few hundred dollars by the mid-2020s, transformed sequencing from a specialized research tool into a broadly deployed measurement technology.

Sanger and Short-Read Sequencing

The first widely adopted sequencing method, developed by Frederick Sanger and colleagues in 1977, uses chain-terminating dideoxy nucleotides to generate a nested set of fragments that are separated by gel electrophoresis and read from fragment length. Sanger sequencing produces reads of roughly 700 to 1,000 bases with very high accuracy and remained the dominant approach through the Human Genome Project, which was completed in 2003. Massively parallel short-read platforms introduced in the mid-2000s, most prominently Illumina's sequencing-by-synthesis chemistry, generate hundreds of millions of 150- to 300-base reads per run. High throughput comes at the cost of read length, which complicates the assembly of repetitive genomic regions. Detailed coverage of these platform generations and their clinical applications appears in PMC research on DNA sequencing methods from past to present.

Long-Read and Single-Molecule Platforms

To address the limitations of short reads, two commercial platforms introduced long-read sequencing in the 2010s. Pacific Biosciences uses single-molecule real-time (SMRT) sequencing, in which a DNA polymerase synthesizes a new strand inside a zero-mode waveguide, and the incorporation of each fluorescently labeled base is detected optically. Oxford Nanopore sequencing threads an individual DNA strand through a protein pore embedded in a membrane; changes in the ionic current as each base passes through the pore identify the sequence. Both methods routinely produce reads of 10,000 to over 100,000 bases, enabling the resolution of structural variants and repetitive elements that short-read assemblies miss. A review of current NGS platform trends and clinical capabilities is available from PMC research on sequencing platforms and applications.

Bioinformatics and Sequence Assembly

Raw sequencing output consists of millions of independent read fragments that must be assembled or aligned to reconstruct the original DNA sequence. De novo assembly algorithms, such as overlap-layout-consensus and de Bruijn graph approaches, piece together reads by identifying overlapping segments. Reference-based alignment uses a known genome as a scaffold to which reads are mapped, allowing efficient variant calling. Signal processing challenges arise throughout: base calling converts raw electrical or optical signals into nucleotide sequences, quality scoring quantifies per-base confidence, and error correction algorithms reduce the elevated error rates characteristic of long-read platforms. The National Center for Biotechnology Information maintains reference resources on molecular biology foundations that underpin sequencing interpretation.

Applications

DNA sequencing has applications in a wide range of fields, including:

• Clinical genomics and rare disease diagnosis through whole-genome or exome sequencing
• Oncology, profiling tumor mutations to guide targeted therapy
• Infectious disease surveillance and outbreak tracking
• Forensic identification and paternity analysis
• Evolutionary biology and population genetics studies