Only a tiny slice of the human genome directly codes for proteins. The rest, once dismissed as “junk DNA,” is now one of the most active areas of modern biology. In humans, about 98% to 99% of DNA is non-coding, meaning it does not contain instructions for making proteins. That number surprises people because genes are often described as the main story of heredity. Genes matter deeply, but they are not the whole book. Much of the genome helps decide when, where, and how stron