Dr. Francis Collins has a knack for making complex things easily understood. Listen as he explains what a gene is as part of the handy Talking Glossary of Genetic Terms. Watch an animation, see an illustration, click to related terms like gene.
It's an interactive journey based on size of objects like a grain of rice, a human egg, the flu virus and a carbon atom. Move the magnifier bar and you are on your way into a world that is small and invisible to the naked eye.