The region of a gene that contains the code for producing the gene's protein. Each exon codes for a specific portion of the complete protein. In some species (including humans), a gene's exons are separated by long regions of DNA (called introns or sometimes "junk DNA") that have no apparent function.

Dr. John Carpten, of the National Human Genome Research Institute's Laboratory of Cancer Genetics, defines exon.

Related terms: gene, genetic code (ATGC), messenger RNA (mRNA), protein.