The problem. You could know DNA carried a linear code (Crick) without being able to read it. Until the late 1970s, determining the actual base-by-base sequence of a piece of DNA was slow, brutal work, there was no general, scalable way to spell out a gene.

The idea. Sanger’s trick is elegant: copy the template with DNA polymerase, but spike in a small fraction of chain-terminating dideoxynucleotides that stop extension whenever they’re incorporated. You get a ladder of fragments ending at every position of a given base; run the four reactions side by side on a gel and read the sequence straight off the rungs. Controlled, random termination turns synthesis into a readout.

Why it matters. This is the headwater of my entire field. Every FASTQ I’ve ever touched, every alignment and variant call, exists because sequencing became routine, and it started here, then scaled through automation, capillary machines, and eventually massively-parallel and nanopore reads. The dideoxy logic even echoes forward: reversible terminators are how Illumina sequences-by-synthesis today.

Verdict. Foundational, and worth reading to see how simple the core idea is beneath decades of engineering. Its limits, short reads, manual gels, low throughput, are exactly what the next fifty years of sequencing technology set out to erase. Read it as the origin point of computational genomics.