The gene is considered the basic unit of inheritance. Genes are passed from parents to offspring and contain the information needed to specify physical and biological traits. Most genes code for specific proteins, or segments of proteins, which have differing functions within the body. Humans have approximately 20,000 protein-coding genes.
The exact definition of the word gene has long been a source of scientific debate. A simple way to think about it is as follows. Proteins are the brick and mortar that make up our cells and tissues. And genes are the part of our genome that encodes the information for making those proteins. For example, the human genome has roughly 20,000 protein-coding genes. Interestingly, all of the information for those 20,000 protein-coding genes is encoded by only 1.5% of the entire human genome. A more expansive definition of a gene includes those segments of DNA that encode information for making an RNA molecule that functions in some fashion other than directly coding for a protein; these are sometimes referred to as RNA genes.
National Human Genome Research Institute