How to Measure Knockout Efficiency in a Cell Pool

Sequence the amplicon. In a pool, amplicon NGS gives the allele distribution — indels, wild type, and larger events — and that distribution is the measurement. A single efficiency number hides the part that matters: whether the indels actually disrupt the protein.

Fast alternatives (Sanger plus ICE/TIDE, restriction digest) are acceptable for triage; they are not sufficient for a claim.

Three pools can all report "70% editing" and behave completely differently:

• • One has 70% frameshift indels — effectively a knockout.
• • One has 70% in-frame indels — partial loss of function at best.
• • One has 70% edited alleles spread across many distinct indels, some of which remove an exon and some of which change one codon.

In cell pools, the practical consequence is that the phenotype you measure is a weighted average over these alleles. Reporting the spectrum, not just the rate, is what makes the result interpretable.

• • Primer placement. Amplicons must cover the cut site with enough flanking sequence to detect larger deletions; amplicons that are too short miss them.
• • Depth. A few thousand reads per sample is adequate for allele frequencies; low depth systematically under-reports rare alleles.
• • Timing. Measure 72 hours or more after editing — early timepoints under-report because editing continues.
• • Cell number. Sequence from a defined number of cells, not from a fraction of the culture, so that the measurement is comparable across arms.

A pool measurement tells you whether the editing strategy works; it does not tell you what any individual clone contains. Before making claims, move to clones and sequence each one — the pool distribution is a planning tool, not a result.

A useful workflow: pool amplicon sequencing to confirm the guide and editing conditions, then clone and sequence 24–96 clones, then select two or more with confirmed null alleles for experiments.

State the method, the amplicon coordinates, the read depth, the timing after editing, and the allele spectrum (top alleles with frequencies), plus the fraction of in-frame versus frameshift events. That combination lets a reader judge whether "knockout" is the right word.

EDITGENE reports amplicon sequencing at pool and clone level, with allele spectra, in-frame versus frameshift classification, and zygosity by digital PCR.

Tell us the target and the cell line. Contact EDITGENE to request a project consultation or quote.

Editing efficiency depends on locus, guide, delivery, and cell type; a pool measurement describes the distribution in that specific experiment.

Indel frequency is not knockout frequency: in-frame indels may retain function, and protein-level confirmation is required for a null claim.

• • Brinkman EK, et al. Easy quantitative assessment of genome editing by sequence trace decomposition. Nucleic Acids Research. 2014;42:e168.
• • Vouillot L, et al. Comparison of T7E1 and surveyor mismatch cleavage assays. G3. 2015;5:407–415.
• • Sentmanat MF, et al. A survey of validation strategies for CRISPR-Cas9 editing. Scientific Reports. 2018;8:888.