1) A length of DNA which codes for the production of one protein
 (Adapted from Edexcel GCSE SCience and Data Resource Book, UG005206) 

2) A segment of DNA that is involved in producing a polypeptide chain; it can include regions preceding and following the coding DNA as well as introns between the exons; it is considered a unit of heredity

» Biology Glossary for 11-16 Yr Olds (Chad Evans)