By Robert Krulwich ABC News Genes don't actually do anything themselves. They hold instructions for making proteins, and it's the proteins that actually perform functions in our bodies. When you look at yourself in a mirror, you're looking mostly at protein.
Proteins are the essence of life.
Because we really like to think of ourselves as a lot more than twice as complex. But humans are far more complex than fruitflies. Genetic scientists suspect that is because our genes are better at making proteins than the genes in a fruitfly. A gene that appears identical in both creatures might produce one or two proteins in a fruitfly, but four in a human being. And in a human those four proteins could combine and interact to make bigger and more proteins.