Your genome is 3 billion letters but only ~20,000 genes
The instruction manual for a human being is written in just four letters — and most of it isn't genes at all.
Every cell in your body carries a near-complete copy of your genome: roughly 3 billion base pairs of DNA, spelled out in just four chemical letters — A, T, C and G. Stretched out, the DNA from a single cell would reach about two metres.
You might expect such a vast code to hold a huge number of genes. It doesn’t. The human genome contains only about 20,000 protein-coding genes — fewer than some plants and roughly the same as a microscopic roundworm.
Those protein-coding genes make up less than 2 percent of the entire genome.
The rest was once dismissed as “junk,” but much of it switches genes on and off, controls timing, and shapes how cells behave. The genome is less a parts list than a layered set of instructions for building and running a body.
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2 referencesWell-established. Corroborated by 2 independent sources.
