A gene is a genetic replicator, a basic unit of heredity in a living organism, and a segment of DNA that is involved in producing proteins. Genes shape life-forms, they are blueprints for biological bodies and recipes for stringing together amino acids into proteins.
The genome of an organism is like a library containing its blueprint, with information in books called chromosomes, and these chromosome books in turn are split into chapters called genes. These libraries contain all the biological information needed to construct and control a whole organism.
- Wikipedia entry for Gene