Deoxyribonucleic acid sequencing is the procedure of reading the right order of base braces, which builds up a Deoxyribonucleic acid. It is a cardinal demand for modern cistron use technique in the molecular field. Evaluation of 3 billion base braces of 24 different chromosomes was a great success in the Human Genome Project. It has helped to uncover 20,000 to 25,000 human cistrons and besides about the controlling parts ( Human Genome undertaking Information, 2008 ) .

The sequencing of the human genome is a milepost in the scientific research, which came easier by measuring related beings with human genome. In 1990, the Human Genome Project has been accomplishable because of modern computing machine installations. Possibly, the comparing and word picture of genome between beings, which contains 1000000s of bases has become world merely with the modern promotion of micro chips and processors. Bioinformatics is the lone stepping rocks for each and every advancement of DNA sequencing undertakings over past two decennaries ( Edmund Pillsbury, n. . ).

This overview discusses about the growing in DNA sequencing undertaking with new engineerings at different periods and how it has reduced the cost of sequencing undertaking. With an betterment Sanger used plus and minus method to sequence 5386 bp phage ? ¤X 174 genome ( Primrose et al. , 2001 ) , but due to the big sum of sample demand, clip and labour intensive nature, genome sequencing research has limited the efforts of sequencing undertaking.

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Later, Sanger has invented a new method of “ scattergun ” sequencing, in which random fragments of Deoxyribonucleic acid from the host genome was isolated and it was used as primers for the PCR elaboration of the whole genome. Then the immediate transcripts are formed by piecing of amplified parts of Deoxyribonucleic acid to the overlapping parts and so the convention primers are exposed at the spreads between the contigs by giving complete sequenced genome. Five old ages subsequently, Sanger used “ scattergun ” method to sequence 48,502 bp, which helped sequencing undertaking to turn at a faster rate.

This rooted a strong foundation to sequence few viral and organellar genomes like 229kb of CMV, 192 kilobit of vaccina, 187 kilobit mitochondrial and 121kb chloroplast genome of Marchantia polymorpha, and the 186 kb genome of variola ( Edmund Pillsbury, n. a. ) . In 1977, Maxam and Gilbert method was widely used in the sequencing undertaking, which involves the basic-specific cleavage of Deoxyribonucleic acid by the use of chemical reagents. With this Maxam and Gilbert method, most big sequences can be sequenced except bacteriophage T7.

Chain eradicator or dideoxy method The concatenation eradicator or dideoxy method depends on the two belongingss of DNA polymerases such as their ability to synthesise a individual isolated complementary transcript of DNA templet and besides depends upon their ability to utilize 2′,3′-dideoxynulceotides as substrates. After the incorporation of parallel at the turning point of the Deoxyribonucleic acid concatenation but the 3 ‘ terminal lacks an OH group and doing the substrate unfit for the concatenation elongation. As a consequence, the turning DNA concatenation is terminated.

In this procedure, dideoxy-nucleotides act as concatenation eradicators ( Primrose et al. , 2001 ) . Edward David Hyman method In 1988, Edward David Hyman has introduced new method for the DNA sequencing, which is apart from the polyacrylamide gel cataphoresis of individual stranded Deoxyribonucleic acid fragments that was generated by any one of the following method such as, concatenation eradicator or dideoxy method, selective enzymatic atomization of RNA or selective chemical debasement of DNA and besides it does non affect any of the radiation or fluorescence method.

The Edward David Hyman method has introduced luciferase-Sepharose column for the first clip to sequence DNA. This method involves mensurating of pyrophosphate generated by DNA polymerisation reaction. The solutions incorporating dNTPs are pumped into a DEAE-Sepharose column, in which DNA and DNA polymerase are held together. As a consequence pyrophosphate is generated, and it is measured continuously by a device incorporating series of columns that are packed with enzymes covalently linked to Sepharose ( Eward David Hyman, 1988 ) .

This method is to the full depends on manual operations and computations and besides requires big sum of chemicals. TIGR assembly program method The Institute of Genomic Research ( TIGR ) has introduced TIGR assembly program package for DNA sequencing in 1990. In this method, genome is fragmented into smaller sections, each of up to 40 kilobit of DNA. Then these fragments are farther broken down to smaller pieces with the aid of shotgun method and so they are sequenced to retrace the genome.

Finally, the research group has met their success by sequencing 1. 8 Mb of H. InfluenzaeA genome. In this undertaking, the undertaking of TIGR assembly program package was to reassemble about 24,000 Deoxyribonucleic acid fragments into the whole genome and this full procedure took 30 hours for the computing machine with 512 Mb RAM ( Edmund Pillsbury, n. a. ) . Automated DNA sequencing method The big polymerase cistron of Sendai virus was used for this method.

This method involves primer with fluorescent dye-labelled dideoxynucleotide eradicators was run on an machine-controlled ABI DNA sequenator. The concluding information of L cistron of Sendai virus has revealed that it contains precisely 6800 bases and the amino acerb sequence of a protein was found to be 252. 876 kDa. As the machine-controlled sequencing method was so fast in the designation of complete sequence, this technique is less economic and clip conserving at those periods ( Gieseckea et al. , 1992 ) . Pseudo-coulometric burden in capillary cataphoresis DNA sequencing

By and large in capillary cataphoresis, the sample volume for the injection should be in the scope of nano liter, which is so hard in lading the sample in such a little volume and besides it is difficult to mensurate the samples so lesser than micro liter. Due to this job we can non lade the full sample for the analysis, merely fraction of the sample can be added to the capillary tubing and furthermore, this will be a great job in the DNA sequencing undertakings because the readying of sequencing sample is so expensive to stack on-column.

This method engages the use of really low ionic strength formamide to re swing the Deoxyribonucleic acid after the precipitation of ethyl alcohol because the formamide increases the electromotive force bead and decreases the electric field in the capillary tubing and therefore forestalling the migration of sample DNA, which helps in long burden periods of the sample without set widening.

Possibly, the formamide increases the motion of big figure of DNA and as the burden becomes a coulometric procedure, the whole procedure has reduced the cost of the whole undertaking. Daniel et al. , 1996 ) Replaceable polymers in DNA sequencing by capillary cataphoresis Few old ages before the care of high-performance DNA sequencing by capillary cataphoresis is extremely economic because the capillary tubings are so sensitive to the drosss and more dearly-won to replace it. Due to the promotion in recent engineerings, this job has been solved by the development of replaceable screening polymers and capillary coatings for the cataphoresis.

Furthermore, the development of electro-osmosis-inhibiting matrix polymers has made the capillary coating procedure rather easier and besides facilitated the mechanization of high-throughput parallel systems for sequencing DNA in large-scale ( Mark A Quesada, 1997 ) . Microfluidic devices for Deoxyribonucleic acid sequencing When the human genome undertaking has become world, all research workers have turned their attending towards cut downing the cost and clip of the genome undertaking.

Few latest engineerings like microfabricated DNA sequencing, sample processing and analysis devices have reached their success in cut downing the clip and cost. The incorporate microfluidic processing has truly reduced the costs, reagents, clip and the use of robotics or any other setup. The microfabricated device involves clone isolation, template elaboration, purification and cataphoretic analysis in its ain fabricated circuit itself and therefore cut downing the cost and clip to the maximal extent ( Brian et al. , 2003 ) .

Multiplexed DNA sequencing-by-synthesis In the multiplexed DNAsequencing-by-synthesis method, the sequences of DNA templets are hybridized to a surface of an immobilized array of Deoxyribonucleic acid primers. They are determined by observing the figure of bases. As each array is encoded with a Xuorescein-labelled deoxyribonucleoside triphosphate ( dNTP ) species, the Deoxyribonucleic acid sequencing can be determined by observing the figure of bases by which primers extend in consecutive DNA polymerase-catalyzed nucleotide reaction.

The labelling on dNTP will be destroyed after each testing with photostimulated reaction by dipheyliodonium chloride. The wrong binding effects were found to be little in this experiment and besides the low degree taint of dNTPs with other bases will bring forth negative signals. The drosss are cleared by polymerase-catalyzed integrating into complementary cleansing semidetached houses. With this method we can readout 6000 bases per minute ( Sergei et al. , 2006 ) Decision

The Human Genome Project is an impossible one before three decennaries but it become existent shortly with the machine-controlled sequencing systems and bioinformatics. Furthermore, the cost, labours, chemicals, clip and setup has been drastically reduced to its maximal extent with the aid of computing machines. This overview has clearly signifies that the DNA sequencing method is turning each and every twelvemonth. Many scientists across the universe are turn outing with their researches, that DNA sequence undertaking is no more expensive at present and it will be cheaper, cut down clip in future.


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