A gene is the basic physical and functional unit of heredity. Genes, which are made up of DNA, act as instructions to make molecules called proteins. In humans, genes vary in size from a few hundred DNA bases to more than 2 million bases. The Human Genome Project has estimated that humans have between 20,000 and 25,000 genes.
Each cell in the human body contains about 25,000 to 35,000 genes. Genes carry the information that determines your traits (say: trates), which are features or characteristics that are passed on to you — or inherited — from your parents.