Next-Generation Sequencing (NGS)
Introduction
Next-Generation Sequencing (NGS) refers to advanced high-throughput sequencing technologies that allow rapid and parallel sequencing of DNA and RNA. Unlike Sanger sequencing, which processes one DNA strand at a time, NGS can sequence millions to billions of fragments simultaneously.
Steps in NGS Workflow
1 DNA/RNA Extraction –
Isolate genetic material from a sample.
2 Library Preparation – Fragment DNA and attach adapters.
3 Amplification – Use PCR or bridge amplification for signal detection.
4 Sequencing – Detect bases via fluorescence, pH, or electrical signals.
5 Data Analysis – Align sequences to a reference genome and interpret
results.
Types of NGS Technologies
1. Illumina Sequencing (Solexa Sequencing)
Uses reversible dye
terminators and bridge amplification on a flow cell.
High accuracy, short read lengths (50-300 bp).
Applications: Whole genome sequencing, RNA-Seq, ChIP-Seq.
2. Roche 454 Pyrosequencing
Measures light emitted
during DNA synthesis.
Longer read lengths (400-800 bp) but lower throughput than Illumina.
Applications: De novo sequencing, metagenomics.
3. Ion Torrent Sequencing
Detects pH changes
when nucleotides are added.
Faster than Illumina but prone to homopolymer errors.
Applications: Targeted sequencing, small genomes.
4. PacBio SMRT (Single-Molecule Real-Time) Sequencing
Uses real-time observation
of DNA polymerase activity.
Produces long reads (up to 100 kb), but higher error rates.
Applications: Structural variation detection, epigenetics.
5. Oxford Nanopore Sequencing
DNA strands pass through a
protein nanopore, and electrical signals are recorded.
Real-time sequencing with ultra-long reads.
Applications: Rapid diagnostics, field-based sequencing.
Applications of NGS
Whole Genome Sequencing (WGS)
– Identify mutations and variants.
Transcriptome Analysis (RNA-Seq) – Study gene expression.
Cancer Genomics – Detect mutations in tumors.
Microbial Sequencing – Identify pathogens and antibiotic resistance.
Personalized Medicine – Tailor treatments based on genetic profiles.
Advantages of NGS
High-throughput sequencing (millions of reads).
Cost-effective for large-scale
projects.
Faster than traditional Sanger
sequencing.
Limitations of NGS
Requires complex bioinformatics
for data analysis.
Short-read technologies may struggle with repetitive regions.