A pooled CRISPR screen knocks out one gene per cell across a whole population simultaneously, then uses a downstream selection to reveal which knockouts change the phenotype being studied.
P(edit) ~ cuttingEff * guide.specificity
hit gene if dropout > selectionPressure
- Guide RNA library — the pooled sgRNA library, typically tiling thousands of guides across the genome.
- Genomic target sites — the specific loci each guide RNA is designed to direct Cas9 toward.
- Cutting efficiency — how reliably Cas9 makes a double-strand break once a guide finds its target.
- Selection pressure — the phenotypic screen (drug resistance, growth, fluorescent reporter) used to reveal which knockouts matter.
Genome-wide CRISPR screens (like the ones from the Broad Institute's GPP) are how researchers systematically discovered synthetic-lethal cancer drug targets that a single-gene hypothesis-driven study would never have found.