| Noun | 1. | mutant gene - a gene that has changed so that the normal transmission and expression of a trait is affected cistron, gene, factor - (genetics) 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; "genes were formerly called factors" CFTR, cystic fibrosis transport regulator - the gene that is mutated in cystic fibrosis |