Next Gen Sequencing [NGS]
• History of DNA Sequencing
• NGS Technologies:
– 454, Illumina, PacBio, ABI, Helicos,
– Ion Torrent, Nanopores
– Genomes, RNASeq, ChIPSeq, CGH, CancerGenome
Human Genome: 1990-2000
Presented by Dominic Suciu, Ph.D.
Preliminaries: Central Dogma
Gene ~ Protein ~ Enzyme
[Program in directory]
[Program in RAM]
~~ Enzyme ~~
BacterioPhages are viruses that infect bacteria
Some Bacteria are immune to certain phages
[Hamilton O. Smith, early 70‟s]
Restriction Endonucleases: Enzymes that specifically
cleave certain DNA sequences.
Bacterial cells use these as a crude anti-phage
Preliminaries: Restriction Enzymes
• Molecular scissors
• Their discovery allowed researchers to physically map genomes
• Big confirmatory clue that Genome sequence determines species and even individuals
Start with picograms of DNA
End up with microgarms of highly purified copies
Each Colony is highly enriched
Each colony is endlessly amplifyable
pBR322: is a vector, an
It can reproduce itself
inside a bacterial host
and do nothing else.
Preliminaries: PCR 
As long as you know
the beginning and
end of a sequence,
you can amplify
• DNA source: gel-purified fragment, cloning
product, random fragmentation.
• DNA Amplification: need enough to be able to detect
signal given off by base interrogation
• DNA Seq Method: Base interrogation method to
uniquely detect G,A,T,C bases.
• Sequence Positioning: Need an organizing principal to
place these bases into a sequence.
The methods presented here represent unique ways to solve each of these issues
• Need perfectly pure single species of DNA
• Nasty Chemicals
• Radioactive End-labeling
• Sequence only what you can purify
- 1st DNA sequencing available
- 2-300 bp/read
Sanger “Sequencing-by-Synthesis” 1977
- Radioactive End-labeling
- Sequencing gels
- 4-500 bp/reads
- Radioactive Incorporation
- Primer gives you control
PCR Dye-Terminator 1990‟s
- Sequencing gels
- 1 run/day
- 600-700 bp/reads
- 96 reads/run
- Each terminator dye has a different
color. Lets you combine all 4 reactions
in one lane.
- Single lane/read
- Primer gives you control
Human Genome Project (15 years) Hierarchical
Shotgun Sequencing [start1990]
- Randomly insert Human DNA into BAC clones (~150kbp each)
- Combine these BAC clones to create a scaffold of the human
genome. Each BAC clone will be mapped to a region on a
- Pass BAC clones to different Genome Centers throughout US
- At each center, each vector is sequenced using shotgun sequencing
- Wait 15 years for results.
Issues with Shotgun Sequencing
• Reads-> contigs -> scaffolds -> genome reconstruction
• Repeat regions can confuse Contig assemblers.
• It was hoped that by focusing each shotgun run to a single 40-150kb region, these
issues would be minimized.
• According to Venter, it simply multiplied the number of times one encountered the
Shotgun Sequencing: Venter 1997
Same approach is used throughout NGS
1. Randomly cut genomic DNA.
2. Use Gel-purification to make three
libraries of random DNA fragments:
2kb, 10kb, 50kb
2. Sequence from both ends.
3. Use distance information to assemble
contigs into scaffolds.
Distance information allows you to
„jump‟ over repeat regions.
This approach allowed Venter to „jump‟
over the federal sequencing project
NGS Revolution: Roche / 454 -> 
ABI 3700 state of the art
- 1 sample per rxn (96
rxns) in 2 hrs
- Each sample had to be
454 solved both these problems
PPi + H+
Paired-end reads can be done by including both primers on each micro-bead
Roche / 454 -> 
• emPCR: No need for
• Each well is a single
• Very fast reaction
Illumina [Solexa 2007]
No need for Cell-based
Bridge Amplification: PCR on
• No need for cells
• Each cluster of DNA
molecules is a single reaction.
• Enormous amounts of reads
• Paired ends Sequence from
• Short reads
• Reagent costs
Ion Torrent/LifeTechnologies 
• Emulsion PCR
• Each bead is placed in a
• Low density
• Sample prep
PPi + H+
• Extremely accurate
• Takes a long time
• Expensive reagent costs
• Whole genome in 3 months
• 40x coverage!!!
• Labor Intensive Takes a long
time: 3 months sample prep
• Expensive: $10-20k/GENOME
• No Instrument: CRO model
• No amplification
Single Molecule Detection
• It doesn‟t work
Applications: Genome Sequencing
Sequencing of whole genomes: bacterial, animal, human.
De novo Genome Sequencing: Even with the large number of
reads, putting a genome together from raw sequence reads is still
a non-trivial task, due to sample prep and inherent complexity.
Sequencing individual with a genetic disease in
order to find hereditary mutations.
Read depth allows one to compute allele-
454: Due to its long reads, this method is best for de novo.
Useful for scaffolding.
SOLiD, Illumina: used for re-sequencing
SOLiD: wins out due to accuracy loses based on
Complete Genomics: CRO model, depth 40x
Applications: Exon Sequencing
Mutational screening: what are the mutations in the actual
Most heritable disease models have mutations in the
Use enrichment to focus sequencing to expressed space.
Then make as many reads as possible in order to
accurately compute mutations.
Illumina, 454, ABI
Enrichment: Microarrays are Not dead!
In order to focus sequencing run on the
region you are interested in.
• Expressed region of genome (1%)
• Genes of interest: mutational studies.
• Micro-droplet PCR: each droplet has
unique set of amplification primers.
• On-chip enrichment, using
• On-bead enrichment: make oligo
pools, use them to capture targets for
Two approaches for finding causative mutation responsible
for Miller Syndrome
Sequence Whole Genome: Complete Genomics
• Sequenced Mother, Father and 2 kids (both affected) 1 kindred
• Regions where they share both copies from parents (22%)
• Both diseases are rare: look for locations with low prevalence
• Narrowed down to 4 genes
• 2 of these were found to be causative agent in exome sequencing
Exome Array: Just sequence expressed sequence space
(1%): Illumina GAII
• Sequenced genomes from 4 affected individuals in 3
• Found 4600 mutants
• Ignored any previously discovered SNPs from dbSNP
• Looked for mutations that appeared in all 3 kindreds
• Focused on damaging mutations Non-synonymous, stop
• Discovered causative locus by elimination
Microarrays are Dead!
Don‟t have to design probes ahead of time, just sequence
mRNA and count number of sequences for each gene.
Read count ~ Expression level
In environmental genomics, sequencing can be used to
determine which genes are being expressed in a sample.
Illumina: Only method that has the read depth to get
useful spread between high and low-expressed
Its Dynamic Range far surpasses microarrays in this
respect, especially for smaller genomes.
ChIP Chromosomal Immune Precipitation
Where does my DNA-
binding transcription factor
bind within the genome?