Variant Limit of Detection: Trace Versus Allele Fraction

Sanger versus NGS for mutation detection is a limit-of-detection job, not a price comparison. Sanger sequencing reports a chromatogram of the majority molecules that primed. NGS reports an allele fraction against a depth budget. Prefer Sanger for a clonal genotype you can read as peaks. Prefer NGS when a minority allele can hide under a clean trace. Reject “the Sanger look is clean, so a 5% variant is absent.”

Sanger versus NGS cost, read length, and turnaround still owns those quote and scale jobs. Coverage versus depth still owns those two words. University core versus commercial Sanger quotes still owns the reaction unit. This page only assigns what each method is allowed to claim about a mutation. Any numeric Sanger minority-allele limit is literature and lab practice, not an official Zetta percentage. Labs often treat small shoulders as unreliable for low-fraction calls. That is a reason to refuse an absence claim. It is not a certified product spec. Do not invent one here.

A Clean Sanger Trace Is Not Proof a Low-Fraction Variant Is Absent

The search compares Sanger and NGS for mutation detection. The entities are detection claims. A Sanger chromatogram is a superposition. If almost all templates carry the same base, the peak looks clean. A minority population can sit under that peak and never become a second letter you are willing to call. NGS, when the library and analysis are appropriate, counts observations at a site. Depth is a budget for how small a fraction you are willing to believe. Those are different sentences you can write in a notebook.

Clone confirmation of a plasmid or a picked colony is often a Sanger job because the intended state is majority. Mosaic edits, mixed clones, residual parental alleles, and somatic minority variants are often an NGS job because absence is the dangerous claim. Mixing the jobs is how a clean trace is pasted into a paper as “no mutation detected” when the method could not have seen the fraction that mattered.

Two Detection Jobs Same Sample Question

Score both methods on the claim you need to write, not on a cheaper-run slogan.

Prefer the chromatogram job when you are accepting or rejecting a clone whose intended genotype should dominate the template. Prefer the allele-fraction job when the scientific claim is “this minority allele is below X,” and X is smaller than a Sanger picture can honestly show. Reject a hybrid sentence that uses Sanger absence to close an NGS-style question. Reject the reverse: an NGS consensus FASTA is not a chromatogram, and a consensus can hide a mixed population if someone only files the majority call.

Do not quote an official Zetta sequencing price. Do not treat a vendor’s marketing LOD as your lab’s LOD without a written depth, error model, and control plan. The 5% in the visible title is a refusal example, not a measured detection limit for every assay.

This Is Not the Cost Page

If the reader is choosing Sanger versus NGS by invoice, read length, or queue, stop and use the cost sibling. If the reader is asking what “30x” means, use the coverage-versus-depth sibling. Stay here only for the detection claim. Method-selection pages that match sequencing to a research question may mention confirmation. They do not own the clean-trace refusal. This page does.

Sanger quote inclusions and primer-on-quote lines are other Wave9 pages. They do not change what a chromatogram is allowed to mean.

A worked refusal: a CRISPR-treated pool is expected to contain a 5% precise-edit allele. A Sanger trace from the pool looks clean at the cut site. That clean picture may mean the majority is unedited. It does not mean the 5% allele is absent. The detection job is NGS with a written depth and an analysis that reports allele fraction, or a clonal isolation step followed by Sanger on picked clones. The opposite fit: a single colony should carry one plasmid genotype. Sanger of the insert is the right detection job. NGS is allowed, but absence of a 5% contaminant is not the question the notebook needs to answer for that colony.

Hold the Confirmed Sequence After the Job Is Named

Name the detection job before anyone files “no variant.” After the job is named, a map workspace such as ZettaGene can hold the confirmed sequence you are willing to claim. That is a place to attach the accepted clone or the named allele after the method’s limit is written. It is not a sequencer, not an official price, and not a LOD certificate. Official product language includes homologous alignment among other molecular tools. It does not replace a chromatogram review or an NGS pileup review.

If the notebook still says “Sanger clean = absent at any fraction,” you do not have a detection rule. You have a picture. Write the claim the method can support. Then file the trace or the counts. Then, if cost is the remaining question, leave this page.

Mosaic tissue and mixed clones are the same detection job wearing different sample names. A founder animal can carry an allele in a minority of cells. An iPSC clone can still be mixed after a “clone” pick. In both cases a clean Sanger trace can describe the majority and still miss the minority that changes the paper’s claim. Write the intended limit before the sample goes to the core. If the claim is clonal identity, Sanger after a true clone pick is in range. If the claim is “below 5% residual parent,” the method must be able to see 5%. Do not invent a Zetta LOD number to finish that sentence.

Frequently Asked Questions

Does a clean Sanger chromatogram prove a minority variant is absent?

No. A clean trace is a majority-allele picture. Low-fraction alleles can sit under that picture. Absence at a small fraction needs a method whose limit matches the claim.

Is this the same decision as Sanger versus NGS cost?

No. Cost and turnaround stay on the sibling. This page only assigns the detection claim.