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.