Every cell in your body - your skin cells, brain cells, blood cells - carries a complete instruction manual for building you. It’s called DNA, and it’s a microscopic code written in just four chemical letters: A, T, G, and C. The full code, called your genome, is about 3 billion letters long.
The code is stored as a long double-helix molecule - two strands twisted around each other. If you unwound and stretched out the DNA from a single one of your cells, it would be about 6 feet long. Yet it fits comfortably inside a microscopic structure called the cell nucleus, which is far smaller than a grain of sand.
Your DNA is nearly the same as everyone else’s - 99.9% identical between any two humans, in fact. The tiny 0.1% that’s different is what makes you uniquely you. Your DNA is also remarkably similar to that of other species: you share about 98% of your DNA with chimpanzees and 85% with mice. Even a banana has rough equivalents for many of your basic genes. All life on Earth shares the same genetic alphabet, written in the same chemical letters.
