Reporter OR Marker Genes - A reporter or marker gene produces a phenotype, which is either easily and specifically detected or which allows a differential multiplication of the cells; the former are called scorable markers, while the latter are known as selectable markers. Scorable markers are used for studying promoter/enhancer activity, while selectable markers are utilized to select for transfected cells.

Examples of scorable markers are chloramphenicol acetyltransferase (CAT) gene from E. coli transposon Tn9, β-galactosidase gene from E. coli and bacterial luciferase gene. The selectable reporter genes are briefly described below.