Genes are the basic physical and functional units of heredity. They consists of a specific sequence of nucleotides at a given position on a given chromosome that codes for a specific protein.
Genes consist of three types of nucleotide sequence: coding regions, called exons, which specify a sequence of amino acids, non-coding regions, called introns, which do not specify amino acids and regulatory sequences, which play a role in determining when and where the protein is made.
