An alternative to a<unk>  is a screenable marker, which allows the researcher to distinguish between wanted and unwanted cells.
Examples of<unk> s include:
the Abicr gene 
Neo gene from Tn5, which confers antibiotic resistance to geneticin
A<unk>  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.<unk> s 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.
Selectable marker
Biased sample
Surrogate endpoint
Genetic marker
Scientific consensus
Quantitative structure-activity relationship
Dose Profile
VACTERL association