What is a genome?
A genome is the complete set of DNA instructions an organism carries, every recipe in the book, plus all the pages in between.
If DNA is the paper and ink, and a gene is a single recipe, the genome is the entire cookbook from cover to cover. Your cells actually carry two cookbooks: a huge main one in the nucleus and a tiny pamphlet inside each mitochondrion.
Why it matters for aging
Your main genome contains about 3 billion DNA letters, stored in the nucleus, the cell's control center. Mitochondria, the power plants of your cells, carry their own separate genome of just 16,569 letters, a leftover from when they were free-living bacteria about two billion years ago.
Why it matters for aging: both genomes collect damage and typos over a lifetime. The small mitochondrial genome is especially exposed, which is why some scientists see it as one of the first things to wear down as we age.
A common myth
Your genome is basically just a list of genes.
Genes, the parts that hold recipes for proteins, make up only around 1 to 2 percent of the human genome. The rest includes switches that control when genes are read, structural regions, and stretches whose purpose scientists are still working out.
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Updated Nov 7, 2026 · All terms