Large Scale And Cost Effective Sequencing Of Genomes Biology Essay

Genome sequencing is one of the most of import Fieldss in scientific discipline and many research were done in this field particularly in human genome.

Genome is biological heredity information in edifice and keeping populating beings. Genome is encoded in deoxyribonucleic acid ( DNA ) which in distinct units known as cistron ( Brooker, 2011 ) . There are assorted types of Deoxyribonucleic acid which is atomic DNA, mitochondrial DNA ( mtDNA ) and chloroplast DNA. This essay will be concentrating on DNA sequencing of atomic DNA for human. Genome sequencing involve procedure known as Deoxyribonucleic acid sequencing which procedure of reading nucleotide bases – A ( A ) , G ( G ) , C ( C ) and T ( T ) in DNA ( Bowman and Sanders, 2012 ) . As genomics DNA unambiguously described a species and an person, DNA sequencing become an of import method for scientist to make research on assorted applications such as evolutionary surveies, happening and aiming cistrons, cloning and many more.

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0 First-generation Sequencing

Deoxyribonucleic acid sequencing engineerings was foremost developed by Frederick Sanger, Walter Gilbert and Allan Maxam in 1970s which known as first-generation sequencing ( Bowman and Sanders, 2012 ) . First-generation sequencing involves two methods which are the chain-termination method developed by Sanger and the chemical sequencing method developed by Gilbert and Maxam. These engineerings consist of three basic phases ; readyings of sample, physical sequencing and familial assemble ( Schadt et al. , 2010 ) . Sample readying involved cloning utilizing polymerase concatenation reaction ( PCR ) to acquire template fragment, the templet than purified and cut into fragments with different sizes and generated signifier same get downing point. The procedure continue with physical sequencing phase utilizing chain-termination method where the fragments are terminated utilizing energy transportation and labeled with one of the four fluorescent dye eradicator and DNA polymerase. All of the fragments will undergo capillary cataphoresis and fluorescence sensing which produce the Deoxyribonucleic acid sequence.

Each of the four dyes corresponds consequently to four different bases. However, this procedure produces low throughput with high cost and clip.


0 Second-generation Sequencing

Second-generation sequencing besides known as next-generation sequencing ( NGS ) and these engineerings are developed in 2000s. The first commercially engineering was Roche 454 released in 2005. Second-generation sequencing besides consist of three phases which are readying of sample, sequencing and imagination, followed by familial assemble and alignment ( Metzker, 2010 ) . Most of second-generation sequencing methods involve finding of DNA sequence by synthesising complementary Deoxyribonucleic acid from DNA templet known as sequencing by synthesis ( SBS ) . Preparation of sample or template normally did utilizing two methods ; individual DNA templets and clonally amplified templet from individual DNA.


1 Roche 454 FLX System

Roche 454 FLX system was released in 2005 by 454 and in 2007, 454 was bought by Roche ( Liu et al. , 2012 ) . In 2008, they released new engineering 454 GS FLX Titanium system. This system usage pyrosequencing engineering which detect releasing of pyrophosphate during nucleotide incorporation. Template readying in Roche 454 FLX system is done utilizing clonally amplified templet method which produces about 100 to 200 1000000s templet. In this method, the Deoxyribonucleic acid templet is in cell free procedure and the adapter that contain cosmopolitan primer site will be ligated to the mark ends which denatured the templet into individual strands DNA. Then, the Deoxyribonucleic acid will be amplified utilizing common PCR primers and will be connected to beads under regulation of one DNA per beads ( Metzker, 2010 ) .

The templet will undergo emulsion PCR and the templets are put in the PicoTiterPlate ( PTP ) good. Each of the bases in the templets strand will match to the 1 of the dNTP and bring forth different coloring material of fluorescent visible radiation. This measure was assisted by add-on of luciferase, sulferylase and luciferin ( Liu et al. , 2012 ) . The visible radiation generated will be detected by CCD camera under the slide and bring forth the DNA sequence. This engineering can read about 230-400 bases.

The advantage of this method is high throughput among the second-generation sequencing and fast run clip. The restrictions are high reagent cost, expensive machine and high mistake in homopolymer repetitions. However, the cost is still relevant and low-cost.

3.2 Ilumina/Solexa GA/HiSeq 2000 system

This system is the most widely used in DNA sequencing field. In 2006, Ilumina launched the Genome Analyzer ( GA ) and in the undermentioned twelvemonth, the company bought by Solexa. In 2010, Solexa released HiSeq 2000 system which has the same sequencing scheme as GA with a few betterments. Ilumina/Solexa GA/HiSeq 2000 system involves readying of templet utilizing clonally amplified templet method, specifically solid-phase elaboration and besides uses the SBS engineering.

In the templet readying phase, indiscriminately distributed bunchs are produced utilizing mate-pair templets through span elaboration. The templets are amplified utilizing PCR and the templets are denatured into individual strand. The clonally amplified bunchs are put on the slide. Following, the samples will undergo four coloring material cyclic reversible expiration ( CRT ) procedure. The slide is flooded with reagent, the base bases are incorporated into DNA strand with different florescent dye and reversible blocked group for each base and. The extra reagent is washed out and followed by imaging to find incorporated bases. Then, the freshly incorporated bases are cleaved and wash once more. This rhythm is repeated until no reaction available.

Each bases label with different dye corresponds to the templet and bring forth different signal and detected by CCD. HiSeq 2000 contains two optical masers and four filters to observe the signal. This engineering can read about 2-150 bases. The advantage of this engineering is really high throughput and the restriction is expensive and low multiplexing ability.

4.0 Third-generation Sequencing


1 PacBio RS system

This system was released by Pacific Boiscience around 2010. This system utilize single-molecule real-time ( SMRT ) technique. In this engineering, DNA synthesis procedure is non crippled alternatively the imagination of incorporation of dye-labeled base onto the complementary templet continue during the DNA synthesis procedure. Therefore, this can be measured straight from DNA polymerase.

The florescent dye is attached non to the base but to the phosphate concatenation. This system contains many SMRT Cells which each have zero-mode wave guide sensors ( ZMW ) nanostructure. The Deoxyribonucleic acid polymerase is confined to the ZMW and the florescent signal is detected utilizing gamma-labeled phosponucleotides. The ZMW merely let the blossoming sensing at the underside of the glass and the DNA polymerase will go on with the primer in order to be read at the underside of ZMW. DNA polymerase will let go of the dye of course when it cleaves the phosphate concatenation and flooded the ZMW array. The fluorescence dye emit coloured light correspond to specific base and this will be detected by the instrument.

The advantages of this engineering are cheaper and faster run clip. This is because SMRT technique merely necessitate minimum reagents and sample readying, Besides, PCR elaboration measure non needed in this engineering which lead to rapid procedure and prevent elaboration prejudice. The other advantage is longer read lengths which is about more than 1000 bases which is due to maximum used of DNA polymerse. The restriction of this engineering is low base on balls truth as this engineering is new and still under development.

Although this engineering rapid, big graduated table and cost-efficient, the second-generation sequencing is still widely used compared to this engineering.

4.2 Nanopore Sequencing

This engineering was started developed in 1995 but until now, the development of this engineering still continues. Nanopore is little holes that use to pull DNA and DNA will go through through the nanopore. The rule is when the nanopore is immersed into conductivity reagent, current will be will be create due to different potency around the nanopore cause by motion of ions. The current green goods varied depends on the size and form of the nanopore.

There is assorted ways than can be used in nanopore sequencing. The nanopore can be made utilizing alpha haemolysin, Mycobacterium smegmatis porin A ( MspA ) and may incorporate blossoming. This engineering will give assorted advantages as the Deoxyribonucleic acid can be straight sequenced utilizing nanopore without the PCR elaboration measure, the labeling measure utilizing chemical and the optical sensor method.

In 2008, Oxford Nanopore Technologies licensed the nanopore sequencing engineerings which use protein nanopore and used the man-made bilayer to make ion motion which lead to production of current. The advantages of this engineering are rapid, big graduated table and cost-efficient as this engineering exclude many procedure and can straight sequencing the Deoxyribonucleic acid. The restriction is this engineering is still under development and unknown truth.

5.0 Decision

Deoxyribonucleic acid sequencing field undergo tremendous technological passage due high demand for rapid, high throughput and low cost for DNA sequencing procedure. Deoxyribonucleic acid sequencing will go on to developed particularly the third-generation sequencing and this will take to assorted new findings and innovation for better hereafter. Second-generation sequencing is still widely used due low truth of third-generation sequencing engineering.


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