For decades after the discovery of DNA, researchers mostly thought of genetics in terms of genes, the pieces or sequences of DNA that encode instructions for building proteins in cells. Then scientists discovered that genes make up just 2 percent of our DNA and that most genetic complexity stems from the vast non-gene code, which influences when genes are turned on or off. Further, half of that non-gene code was found to come from insertions of viral DNA. Consequently, say the authors, genetic variation, and the potential for disease-causing mistakes, occurs in transposons as well as in genes.

New laboratory techniques can identify which of our genes are influenced by DNA snippets that are left behind in our genetic code by viruses, a new study finds.