The study of transposons by biologists provides a fresh understanding of these organisms, the knowledge that may one day aid in the battle against cancer and age-related disorders. They are considered ‘parasitic genes’. Even though they comprise over half of human DNA, much remains to be learned about them. Now University of California, Irvine biologists offer new insights into these entities known as transposons, providing knowledge that could one day help in the fight against cancers and ageing-related diseases. Unlike genes that encode proteins needed for us to function, transposons make proteins solely to copy their own DNA and insert it into other elements. “They are selfish parasites,” said study leader Grace Yuh Chwen Lee, assistant professor of ecology and evolutionary biology. “They perpetuate themselves and, most of the time, they don't do anything for us.” Almost all species contain transposons and have developed chemical modifications that stop their continued replication. But the percentage of transposons varies widely across genomes. It ranges from 50 per cent in humans and 65 per cent in salamanders to just six per cent in puffer fish. Even among different kinds of fruit flies, the figure varies from two to 25 per cent.