Comparing DNA Sequencing Methods

What sequencing method and signal does Sanger sequencing use?

Fluorescent ddNTP chain termination followed by capillary electrophoresis.

• Fragment size and dye color identify each base.

Does Sanger use clonal amplification or real-time sequencing, and what is its typical scale?

Neither, Sanger sequences a prepared template and is not real time sequencing. Reads are about 500-1,000 bp, very accurate, and low throughput.

What is Sanger best used for, and what limits it?

It is best for variant validation, plasmids, clones, and small targeted regions. Though, it is slow and expensive per base.

What sequencing method and signal does Oxford Nanopore use?

It passes DNA or RNA through a protein pore and measures sequence-dependent ionic-current changes. Software converts the electrical signal into bases.

Does Oxford Nanopore require clonal amplification, and what read profile does it produce?

It does not require clonal amplification; it can sequence molecules directly in real time. Reads are commonly tens of kilobases (kb) and can exceed 100 kb, but raw accuracy is more variable.

What is Oxford Nanopore best used for, and what limits it?

It is useful for portable field sequencing, ultra-long reads, structural variants, direct RNA, and some epigenetics. Homopolymers and raw-read errors can be challenging.

What sequencing method and signal does PacBio HiFi use?

A polymerase copies a circular SMRTbell template in real time, and fluorescent incorporations are observed in zero-mode waveguides.

Does PacBio HiFi use clonal amplification, and what read profile does it produce?

No; it sequences individual molecules and makes a consensus from multiple passes. HiFi reads are commonly 10-25 kb with accuracy often above 99.9%.

What is PacBio HiFi best used for, and what is its trade-off?

It is excellent for genome assembly, structural variants, phasing, and full-length transcripts. Though, it costs more per base and yields less output than Illumina.

What sequencing method and signal does Illumina sequencing by synthesis use?

It sequences clonal DNA clusters one base at a time using fluorescent reversible terminators and imaging after each cycle.

Does Illumina use amplification, and what read profile does it produce?

It uses bridge amplification on a flow cell and is not real time. It produces short 50-300 bp reads but millions to billions of accurate reads per run.

What is Illumina best used for, and what limits it?

It is best for high-depth variant detection, RNA-seq, resequencing, and many samples. However, short reads make repeats, complex variants, and de novo assembly harder to resolve.

Which platform should you choose for a suspected mutation in a plasmid?

Sanger sequencing. it is highly accurate and practical for a small targeted region.

Which platform should you choose for portable real-time sequencing with the longest possible reads?

Oxford Nanopore. it is portable, real time, and can generate ultra-long reads.

Which platform should you choose for a complex genome assembly requiring long reads with the highest consensus accuracy?

PacBio HiFi. long, highly accurate consensus reads support assembly and phasing.

Which platform should you choose for inexpensive high-depth sequencing of many samples?

Illumina. its massive throughput provides low cost per base.

How does Sanger sequencing compare with Illumina in read length and throughput?

Sanger usually produces longer individual reads, about 500-1,000 bp, but very low throughput. Illumina produces much shorter reads, often 50-300 bp per end, at massively higher throughput.

How does Oxford Nanopore compare with PacBio HiFi in read length and accuracy?

Nanopore can produce longer and ultra-long reads, but its raw-read accuracy is more variable. PacBio HiFi commonly produces 10-25 kb reads with very high consensus accuracy, often above 99.9%.

How does Illumina differ from PacBio HiFi in the type of sequencing problem each solves best?

Illumina is strongest for inexpensive, high-depth short-read studies with many samples. PacBio HiFi is stronger when long, highly accurate reads are needed to resolve haplotypes, assemblies, and structural variants.

How does Oxford Nanopore differ from Illumina in timing and portability?

Nanopore can provide real-time results and is available in portable formats. Illumina is a cycle-based, image-driven platform designed for high-throughput laboratory sequencing.

What do Sanger, PacBio HiFi, and Illumina all have in common in how they identify bases?

They all use fluorescence to identify bases or nucleotide incorporations. Sanger identifies fluorescently labeled terminated fragments, PacBio observes fluorescent incorporations, and Illumina images fluorescent reversible terminators.

Which platform in this comparison identifies bases electrically rather than optically?

Oxford Nanopore. It measures ionic-current changes as nucleic acid passes through a nanopore.

Which platforms are most useful when you need to span a structural variant or repetitive region, and why?

PacBio HiFi and Oxford Nanopore are most useful because their long reads can span complex regions. Illumina's short reads often cannot connect sequence across long repeats or complex variants.

What is the main distinction between a raw Nanopore read and a PacBio HiFi read?

A raw Nanopore read is typically a single electrical-signal-based read whose accuracy depends strongly on basecalling and chemistry. A PacBio HiFi read is a high-accuracy consensus created from multiple passes around the same circular template.