Screen Type Terms

Term	Description
Negative Selection	Screen for identifying genes whose perturbation results in cells not surviving the selection mechanism. Typically, the associated phenotype is “viability” or “resistance” and the mutants are underrepresented/depleted after selection. This fitness screen may be used to determine gene essentiality. May also be referred to as a dropout screen.
Positive Selection	Screen for identifying genes whose perturbation results in cells surviving the selection mechanism, e.g drug exposure. Typically, the associated phenotype is “viability” or “resistance” and the mutants are overrepresented/enriched after selection. This fitness screen may be used to detect drug resistance and identify drug targets. Also known as an enrichment screen.
Positive and Negative Selection	Screen for identifying genes whose perturbation results in either increased resistance or increased sensitivity to the selection mechanism, e.g drug exposure. Typically, the associated phenotype is “viability” or “resistance” and the mutants are those that are either significantly overrepresented/enriched OR underrepresented/depleted after selection in a single screen.
Phenotype Screen	Screen for identifying genes whose perturbation results in other non-fitness phenotypes, such as altered nuclear size or detection of a selectable marker for measuring activity of a particular pathway.