A selectable marker is a gene introduced into cells, especially bacteria or cells in culture, which confers one or more traits 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 transformation or other procedure meant to introduce foreign DNA into a cell. Selectable markers are often antibiotic resistance genes: bacteria subjected to a procedure by which exogenous DNA containing an antibiotic resistance gene (usually alongside other genes of interest) has been introduced are grown on a medium containing an antibiotic, such that only those bacterial cells which have successfully taken up and expressed the introduced genetic material, including the gene which confers antibiotic resistance, can survive and produce colonies. The genes encoding resistance to antibiotics such as ampicillin, chloramphenicol, tetracycline, kanamycin, etc., are all widely used as selectable markers for molecular cloning and other genetic engineering techniques in E. coli.