A
selectable marker is a
gene introduced into a
cell, especially a
bacterium or to cells in
culture, that confers a trait suitable for
artificial selection. They are a type of
reporter gene used in laboratory
microbiology,
molecular biology, and
genetic engineering to indicate the success of a
transfection or other procedure meant to introduce foreign
DNA into a cell. Selectable markers are often
antibiotic resistance genes; bacteria that have been subjected to a procedure to introduce foreign DNA are grown on a medium containing an antibiotic, and those bacterial
colonies that can grow have successfully taken up and
expressed the introduced genetic material. Normally the genes encoding resistance to antibiotics such as
ampicillin, chloroamphenicol, tetracycline or kanamycin, etc., are considered useful selectable markers for E.coli.