What is dna sequencing

DNA sequencing determines the order of the four chemical building blocks - called "bases" - that make up the DNA molecule. Sequencing DNA means determining the order of the four chemical building blocks - called "bases" - that make up the DNA molecule.

The sequence tells scientists the kind of genetic information that is carried in a particular DNA segment. For example, scientists can use sequence information to determine which stretches of DNA contain genes and which stretches carry regulatory instructions, turning genes on or off.

In addition, and importantly, sequence data can highlight changes in a gene that may cause disease. In the DNA double helix, the four chemical bases always bond with the same partner to form "base pairs.

This pairing is the basis for the mechanism by which DNA molecules are copied when cells divide, and the pairing also underlies the methods by which most DNA sequencing experiments are done.

The human genome contains about 3 billion base pairs that spell out the instructions for making and maintaining a human being. Since the completion of the Human Genome Project, technological improvements and automation have increased speed and lowered costs to the point where individual genes can be sequenced routinely, and some labs can sequence well over , billion bases per year, and an entire genome can be sequenced for just a few thousand dollars.

One new sequencing technology involves watching DNA polymerase molecules as they copy DNA - the same molecules that make new copies of DNA in our cells - with a very fast movie camera and microscope, and incorporating different colors of bright dyes, one each for the letters A, T, C and G. This method provides different and very valuable information than what's provided by the instrument systems that are in most common use.

Each genome contains all of the information needed to build that organism and allow it to grow and develop. Its development has helped to dramatically advance our understanding of genetics. DNA or deoxyribonucleic acid is a long molecule that contains our unique genetic code.

Like a recipe book it holds the instructions for making all the proteins in our bodies. If you have any other comments or suggestions, please let us know at comment yourgenome. Can you spare minutes to tell us what you think of this website? Open survey. In: Stories Methods and Technology. Human chromosomes range in size from about 50,, to ,, base pairs Human chromosomes range in size from about 50,, to ,, base pairs and each human being has 46 23 pairs of these chromosomes. We can now sequence an entire human genome in a matter of hours.

Related Content:. The dawn of DNA sequencing. The two scientists in the photograph are reading the genetic code for a DNA sample on a highlighted light board.

Such analysis is usually done by a computer. Credit: National Cancer Institute. DNA sequencing played a pivotal role in mapping out the human genome, completed in , and is an essential tool for many basic and applied research applications today. It has for example provided an important tool for determining the thousands of nucleotide variations associated with specific genetic diseases, like Huntington's, which may help to better understand these diseases and advance treatment.

DNA sequencing also underpins pharmacogenomics. This is a relatively new field which is leading the way to more personalised medicine. Pharmacogenomics looks at how a person's individual genome variations affect their response to a drug.

Such data is being used to determine which drug gives the best outcome in particular patients. Over drugs approved by the FDA now include pharmacogenomic information in their labelling. Such labelling is not only important in terms of matching patients to their most appropriate drug, but also for working out what their drug dose should be and their level of risk in terms of adverse events.

Individual genetic profiling is already being used routinely to prescribe therapies for patients with HIV, breast cancer, lymphoblastic leukaemia and colon cancer and in the future will be used to tailor treatments for cardiovascular disease, cancer, asthma, Alzheimer's disease and depression.

Drug developers are also using pharmacogenomic data to design drugs which can be targeted at subgroups of patients with specific genetic profiles.

Although scientists established DNA had a double helix structure in , it was to be many more years before they could analyse DNA fragments. In part this reflected the fact that small DNA molecules contain several thousands of nucleotides and it was difficult to obtain large quantities of homogeneous DNA.

Scientists also lacked the means to degrade DNA which they needed for sequence analysis. A new chapter opened up in the s with the emergence of techniques to sequence ribonucleic acid RNA s. Critically, Wu's approach broke the DNA sequence down into several different components for analysis, thereby circumventing the need for large quantities of homogeneous DNA.

Subsequently, in , Wu demonstrated his method could sequence the ends of DNA in lambda phage, and two years later that it had the capacity to determine the sequence of any DNA. In Sanger, together with Alan Coulson, published what became known as the 'Plus and Minus' technique. This enabled the sequencing of up to 80 nucleotides in one go.

Three years later, in , Sanger and his colleagues announced another technique called the 'Sanger method' or 'dideoxy sequencing'. This made it possible to sequence much longer stretches of DNA very rapidly. Their approach appeared alongside the reporting of another technique by Allan Maxam and Walter Gilbert at Harvard University.

While the Maxam-Gilbert method initially proved the most popular, it soon fell out of favour because it necessitated the use of hazardous chemicals and radioisotopes. Added to this, the method it was difficult to scale-up and could not be used in standard molecular biology kits because of its technical complexity. By contrast, the Sanger method gained popularity because it was easier to use and more reliable.

It was also amenable to automation, paving the way to the first generation of automated DNA sequencers. These machines used capillary electrophoresis rather than gel electrophoresis using slabs. Several new DNA sequencing methods and machines have been developed since the s. These were built following the introduction of microfluidic separation devices which improved sample injection and speeded up separation times.

Such innovations improved both the efficiency and accuracy of sequencing, allowing for high-throughput sequencing, and radically lowered the cost. Several methods have been developed for this process. These have four key steps.

In the first instance DNA is removed from the cell. This can be done either mechanically or chemically. The second phase involves breaking up the DNA and inserting its pieces into vectors, cells that indefinitely self-replicate, for cloning. In the third phase the DNA clones are placed with a dye-labelled primer a short stretch of DNA that promotes replication into a thermal cycler, a machine which automatically raises and lowers the temperature to catalyse replication.

The final phase consists of electrophoresis, whereby the DNA segments are placed in a gel and subjected to an electrical current which moves them. Originally the gel was placed on a slab, but today it is inserted into a very thin glass tube known as a capillary. When subjected to an electrical current the smaller nucleotides in the DNA move faster than the larger ones. Electrophoresis thus helps sort out the DNA fragments by their size. The different nucleotide bases in the DNA fragments are identified by their dyes which are activated when they pass through a laser beam.

All the information is fed into a computer and the DNA sequence displayed on a screen for analysis. The method developed by Sanger was pivotal to the international Human Genome Project.

Data from the project provided the first means to map out the genetic mutations that underlie specific genetic diseases. It also opened up a path to more personalised medicine, enabling scientists to examine the extent to which a patient's response to a drug is determined by their genetic profile.

The genetic profile of a patient's tumour, for example, can now be used to work out what is the most effective treatment for an individual. Data from the the Human Genome Project has also helped fuel the development of gene therapy, a type of treatment designed to replace defective genes in certain genetic disorders. In addition, it has provided a means to design drugs that can target specific genes that cause disease. Beyond medicine, DNA sequencing is now used for genetic testing for paternity and other family relationships.

It also helps identify crime suspects and victims involved in catastrophes. The technique is also vital to detecting bacteria and other organisms that may pollute air, water, soil and food. In addition the method is important to the study of the evolution of different population groups and their migratory patterns as well as determining pedigree for seed or livestock. Victor Ingram breaks the genetic code behind sickle-cell anaemia using Sanger's sequencing technique.

First comprehensive protein sequence and structure computer data published as 'Atlas of Protein Sequence and Structure'. Process called repair replication for synthesising short DNA duplexes and single-stranded DNA by polymerases is published. Nobel Prize given in recognition of discovery of restriction enzymes and their application to the problems of molecular genetics.

BRCA1, a single gene on chromosome 17, shown to be responsible for many breast and ovarian cancers. Method devised to isolate methylated cytosine residues in individual DNA strands providing avenue to undertake DNA methylation genomic sequencing. Publication of complete genome sequence of the first multicellular organism, the nematode worm Caenorhabditis elegans. Complete sequences of the genomes of the fruit fly Drosophila and the first plant, Arabidopsis, are published.

Paper published demonstrating possibility of using ion channel to identify individual DNA hairpin molecules. First time four bases of DNA shown to be easily identified using engineered alpha-haemoplysin pore with a molecular adaptor.

Oxford Nanopore Technology decides to focus its resources on developing nanopore sequencing for DNA sequencing. DNA sequencing proves useful to documenting the rapid evolution of Streptococcus pneumococci in response to the application of vaccines.

DNA sequencing utilised for identifying neurological disease conditions different from those given in the original diagnosis. MinION successfully used to sequence Ebola virus samples in Guinea to help combat outbreak of the disease.

High throughput nanopore sequencing device PromethION 48 launched to support population genomics for human sequencing or plant genomics. Oxford Nanopore Technology's sequencing technology chosen for a population genome genomics programme for the first time Abu Dhabi Genome Programme. Respond to or comment on this page on our feeds on Facebook , Instagram or Twitter.

Facebook Twitter Donate to WiB. DNA Sequencing Definition DNA sequencing is a method used to determine the precise order of the four nucleotide bases — adenine, guanine, cytosine and thymine - that make up a strand of DNA. He was also pivotal to the development of the dideoxy chain-termination method for sequencing DNA molecules, known as the Sanger method.

This provided a breakthrough in the sequencing of long stretches of DNA in terms of speed and accuracy and laid the foundation for the Human Genome Project. He was also instrumental in the application of genetic engineering to agricultural plants to improve their output and resistance to pests, salt and drought.

He shared the Nobel Prize in for helping to discover restriction enzymes and showing their application in molecular genetics. It was based on some work he carried out in the s.

Arber indicated in that restriction enzymes could be used as a tool for cleaving DNA. The enzymes are now an important tool for genetic engineering. In she completed the sequence of the poliovirus, the longest piece of eukaryotic DNA to be sequenced at that time. She devoted her life to understanding the Epstein-Barr virus, the cause of Burkitt's Lymphoma, a deadly form of cancer. This he achieved with Kent Wilcox in Smith was awarded the Nobel Prize for Physiology or Medicine in for his part in the discovery of the enzyme.

It was the first bacterial genome to be deciphered. Later on he helped in the genomic sequencing efforts for the fruit fly and humans at Celera Genomics. He was involved in some of the early efforts to pioneer techniques for determining base sequences in nucleic acids, known known as DNA sequencing, for which he shared the Nobel Prize for Chemistry in He was the first scientist to propose the existence of intron and exons.

In Gilbert became a proponent of the theory that the first forms of life evolved out of replicating RNA molecules. The same year he began campaigning to set up the Human Genome Project.

He was also a co-founder and the first Chief Executive Officer of Biogen, a biotechnology company originally set up to commercialise genetic engineering. Thesis: 'On the metabolism of the amino acid lysine in the animal body'. It was the first animal to have its genome sequenced. Based on his work with the nematode, Sulston helped set up the project to sequence the human genome which he did as director of the Sanger Centre. The first draft of the human genome sequence was completed in In he shared the Nobel Prize for identifying how genes regulate the life cycle of cells through apoptosis.

His work is initially supported by a Beit Memorial Fellowship from and then by Medical Research Council from In Venter worked with a team to create the first form of synthetic life. This involved synthesising a long molecule of DNA that contained an entire bacerum genome and then inserting this into another cell. The technique Sanger develops for sequencing insulin later becomes known as the degradation or DNP method.

It was the result of a collective effort led by Margaret Dayhoff to co-ordinate the ever-growing amount of information about protein sequences and their biochemical function. It provided the model for GenBank and many other molecular databases.

Arber, 'Host-controlled modification of bacteriophage', Annual Review Microbiology, 19 ,