Structurally, a basic unit of hereditary material; an ordered @[email protected] of @[email protected] 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 (@[email protected]) between individual coding segments (@[email protected]). Functionally, the gene is defined by the [email protected]@ test that determines whether independent @[email protected] of the same @[email protected] occur within a single gene or in several genes involved in the same function.