Structurally, a basic unit of hereditary material; an ordered @ST06775@ of @N04254@ that encodes one polypeptide chain (via mRNA). The gene includes, however, regions preceding and following the coding region (leader and trailer) as well as (in eukaryotes) intervening sequences (@I03141@) between individual coding segments (@E02268@). Functionally, the gene is defined by the cis-@C01092@ test that determines whether independent @M04074@ of the same @P04542@ occur within a single gene or in several genes involved in the same function.