Copy target DNA 2. The method enables microbiologists to evaluate bacterial diversity and detect the abundance of microbes in various environments. Edwards, A; Caskey, T (1991). Add new content to your site from Sensagent by XML. The subject of DNA sequencing theory addresses the relationships of such quantities. Funding came from the US government through the National Institutes of Health in the United States, and a UK charity organization, … Hierarchical Shotgun sequencing In whole genome shotgun sequencing (top), the entire genome is sheared randomly into small fragments (appropriately sized for sequencing) and then reassembled. The web service Alexandria is granted from Memodata for the Ebay search. This can be done for instance by mechanically shearing DNA and then building a set of shotgun sequencing jobs which are then compiled back together by a genome assembler (i.e. Merge into consensus sequence Hierarchical Shotgun Sequencing • Sequencing each BAC lets you – … There are two general strategies for sequencing a complete genome. Each fragment in the library is partially sequenced. If the gap is small (5-20kb) then the use of PCR to amplify the region is required, followed by sequencing. The public effort to sequence the human genome initially employed a hierarchical shotgun strategy based on shotgun sequencing of mapped large-insert clones. Two principal methods are used for this: chromosome walking, which progresses through the entire strand, piece by piece, and shotgun sequencing, which is a faster but more complex process, and uses random fragments. [1] Broader application benefited from pairwise end sequencing, known colloquially as double-barrel shotgun sequencing. The major disadvantage is that the accuracies are usually lower (although this is compensated for by the high coverage).[14]. The hope is that there will be some overlap with the fragments. As sequencing projects began to take on longer and more complicated DNAs, multiple groups began to realize that useful information could be obtained by sequencing both ends of a fragment of DNA. Hierarchical shotgun sequencing creates a physical map of the genome; hence, it produces genomic landmarks that can be helpful in sequence assembly if the genome is rich in repetitive sequences (like the human genome). [9] Historically, full-genome shotgun sequencing was believed to be limited by both the sheer size of large genomes and by the complexity added by the high percentage of repetitive DNA (greater than 50% for the human genome) present in large genomes. ○   Lettris Shotgun sequencing: An approach used to decode a genome by shredding ("shotgunning") it into smaller fragments of DNA which can then be individually sequenced. Most English definitions are provided by WordNet . Even so, current methods have failed to isolate or assemble reliable sequence for approximately 1% of the (euchromatic) human genome[citation needed]. Shotgun vs. Hierarchical Method Celera vs. Human Genome Project Hierarchical (top-down) assembly: – The genome is carefully mapped – “Shotgun” into large chunks of 150kb • Exact location of each chunk is known – Each piece is again “shotgun” into 2kb and sequenced The sequences of these fragments are then ordered, based on overlaps in the genetic code, and finally reassembled into the complete sequence. Although shotgun sequencing can in theory be applied to a genome of any size, its direct application to the sequencing of large genomes (for instance, the human genome) was limited until the late 1990s, when technological advances made practical the handling of the vast quantities of complex data involved in the process. "Next Generation Sequencing: From Basic Research to Diagnostics". In this approach, genomic DNA is cut into pieces of about 150 Mb and inserted into BAC vectors, transformed into E. coli … Then known segment of marked chromosome are cloned in plasmids. Ro, Cookies help us deliver our services. Get XML access to fix the meaning of your metadata. To hasten the sequencing process, in 1979 Staden proposed the idea of ‘shotgun sequencing’, where bacterial vectors are used to clone random fragments of a long DNA molecule. Find a subset of BACs that cover target DNA 5. Since the chain termination method of DNA sequencing can only be used for fairly short strands (100 to 1000 basepairs), longer sequences must be subdivided into smaller fragments, and subsequently re-assembled to give the overall sequence. Depending on the size of the gap between contigs, different techniques can be used to find the sequence in the gaps. "Automated DNA sequencing of the human HPRT locus". A BAC contig that covers the entire genomic area of interest makes up the tiling path. "Whole-genome random sequencing and assembly of Haemophilus influenzae Rd". Fleischmann, RD; et al. Company Information "The genome sequence of Drosophila melanogaster". Change the target language to find translations.  | Last modifications, Copyright © 2012 sensagent Corporation: Online Encyclopedia, Thesaurus, Dictionary definitions and more. Although the sequencing of the human genome is not yet absolutely complete, it is estim… It is named by analogy with the rapidly expanding, quasi-random firing pattern of a shotgun.  |  In reality, this process uses enormous amounts of information that are rife with ambiguities and sequencing errors. In 1995 Roach et al. Each sequence is called an end-read or read and two reads from the same clone are referred to as mate pairs. Physical coverage is the average number of times a base is read or spanned by mate paired reads.[8]. [12] Overlapping clones can be identified in several ways. Sequencing strategies. Although shotgun sequencing was the most advanced technique for sequencing genomes from about 1995–2005, other technologies have surfaced, called next-generation sequencing. The original sequence is reconstructed from the reads using sequence assembly software. Shotgun sequencing involves randomly breaking up DNA sequences into lots of small pieces and then reassembling the sequence by looking for regions of overlap. A high coverage in shotgun sequencing is desired because it can overcome errors in base calling and assembly. Contigs can be linked together into scaffolds by following connections between mate pairs. Shotgun sequencing is the method used to sequence the human genome by Craig Venter at Celera Genomics. Clone based sequencing In clone based sequencing (also known as hierarchical shotgun sequencing) the first step in mapping. Meaning of shotgun sequencing. For example, a hypothetical genome with 2,000 base pairs reconstructed from 8 reads with an average length of 500 nucleotides will have 2x redundancy. The v short answer is that in shotgun sequencing, the sequencer is fed a set of random sequences from the target. [10] In hierarchical sequencing, also known as top-down sequencing, a low-resolution physical map of the genome is made prior to actual sequencing. ©1996-2021 MedicineNet, Inc. All rights reserved. Shotgun sequencing In genetics , shotgun sequencing is a method used for sequencing random DNA strands. The genomic positions of the cloned fragments had been defined prior to shotgun cloning, making their shotgun sequence assembly easier. This article incorporates public domain material from the National Center for Biotechnology Information document "NCBI Handbook". … See if you can get into the grid Hall of Fame ! The method preferred by the Human Genome Project is the hierarchical shotgun sequencing method. It may not have been reviewed by professional editors (see full disclaimer). Shotgun sequencing is when a genomic library is constructed by ligating random genomic DNA fragments into a vector, and then randomly sequencing these clones. In shotgun sequencing,[1][2] DNA is broken up randomly into numerous small segments, which are sequenced using the chain termination method to obtain reads. All rights reserved. shotgun sequencing (Noun) A DNA sequencing technique in which a large number of small fragments of a long DNA strand are generated at random, sequenced, and reassembled to form a sequence of the original strand. [11] Because it involves first creating a low-resolution map of the genome, hierarchical shotgun sequencing is slower than whole-genome shotgun sequencing but relies less heavily on computer algorithms for genome assembly than whole-genome shotgun sequencing. From this map, a minimal number of fragments that cover the entire chromosome are selected for sequencing. The method preferred by the Human Genome Project is the hierarchical shotgun sequencing method. Sequence each fragment with shotgun 2. One major use of genomic libraries is hierarchichal shotgun sequencing, which is also called top-down, map-based or clone-by-clone sequencing. Edwards, A; Voss, H.; Rice, P.; Civitello, A.; Stegemann, J.; Schwager, C.; Zimmerman, J.; Erfle, H.; Caskey, T.; Ansorge, W. (1990). The "whole genome shotgun" method is applied to the entire genome all at once, while the "hierarchical shotgun" method is applied to large, overlapping DNA fragments of known location in the genome. Multiple overlapping reads for the target DNA are obtained by performing several rounds of this fragmentation and sequencing. ©1996-2020 MedicineNet, Inc. All rights reserved. This scaffold is called a tiling path. The SensagentBox are offered by sensAgent. It is named by analogy with the rapidly expanding, quasi-random firing pattern of a shotgun . Shotgun sequencing. Hierarchical Shotgun sequencing is one method of sequencing. Proponents of this approach argue that it is possible to sequence the whole genome at once using large arrays of sequencers, which makes the whole process much more efficient than more traditional approaches. After the order of these segments is deduced, they are further sheared into fragments appropriately sized for sequencing. Many overlapping reads for each segment of the original DNA are necessary to overcome these difficulties and accurately assemble the sequence. [11] In this way, the minimum amount of high-throughput sequencing and assembly is required. The process of extensive BAC library creation and tiling path selection, however, make hierarchical shotgun sequencing slow and labor intensive. There are two general strategies for sequencing a complete genome. It is also called clone-by-clone sequencing due to the use of BAC clones as a source [3,4]. Once the overlap between the clones has found and their order relative to the genome known, a scaffold of a minimal subset of these contigs that covers the entire genome is shotgun-sequenced. English: In whole genome shotgun sequencing (top), the entire genome is sheared randomly into small fragments (appropriately sized for sequencing) and then reassembled. [4] At the time, there was community consensus that the optimal fragment length for pairwise end sequencing would be three times the sequence read length. English Encyclopedia is licensed by Wikipedia (GNU). cloning all DNA fragments of a genome into cleaved vectors at a time by a single cloning experiment is called shotgun cloning. The chain termination method of DNA sequencing (or "Sanger sequencing" for its developer Frederick Sanger) can only be used for fairly short strands of … Get XML access to reach the best products. The first theoretical description of a pure pairwise end sequencing strategy, assuming fragments of constant length, was in 1991. Although sequencing both ends of the same fragment and keeping track of the paired data was more cumbersome than sequencing a single end of two distinct fragments, the knowledge that the two sequences were oriented in opposite directions and were about the length of a fragment apart from each other was valuable in reconstructing the sequence of the original target fragment. Because multiple genome copies have been sheared at random, the fragments contained in these clones have different ends, and with enough coverage (see section above) finding a scaffold of BAC contigs that covers the entire genome is theoretically possible. Make BAC library 3. Metzker, Michael L. (2010). ○   Boggle. ○   Anagrams Now that the technology is available and the reliability of the data demonstrated,[10] the speed and cost efficiency of whole-genome shotgun sequencing has made it the primary method for genome sequencing. Venter, J. C. ‘’Shotgunning the Human Genome: A Personal View.’’ Encyclopedia of Life Sciences, 2006. Shotgun sequencing was one of the precursor technologies that was responsible for enabling full genome sequencing. The English word games are: It can be calculated from the length of the original genome (G), the number of reads(N), and the average read length(L) as . MedicineNet does not provide medical advice, diagnosis or treatment. Adams, MD; et al. The clones are then sequenced from both ends using the chain termination method yielding two short sequences. This entry is from Wikipedia, the leading user-contributed encyclopedia. in whole genome sequencing projects) into a full sequence. The sequences of these fragments are then ordered, based on overlaps in the genetic code, and finally reassembled into the complete sequence.. Shotgun cloning method is widely adopted to create genomic DNA libraries. The gut microbiome of long-lived people display an increasing abundance of subdominant species, as well as a rearrangement in health-associated bacteria, but less is known about microbiome functions. Whole genome shotgun sequencing for small (4000 to 7000 basepair) genomes was already in use in 1979. ), "A strategy of DNA sequencing employing computer programs", "Shotgun DNA sequencing using cloned DNase I-generated fragments", http://www.nature.com/nrg/journal/v11/n10/fig_tab/nrg2841_F1.html, http://www.the-scientist.com/news/20021231/06, "Shotgun sequencing finds nanoorganisms - Probe of acid mine drainage turns up unsuspected virus-sized Archaea", http://www.spaceref.com/news/viewpr.rss.html?pid=21532, National Center for Biotechnology Information, http://en.wikipedia.org/w/index.php?title=Shotgun_sequencing&oldid=497290069. The distance between contigs can be inferred from the mate pair positions if the average fragment length of the library is known and has a narrow window of deviation. The chain termination method of DNA sequencing "Sanger sequencing" can only be used for short DNA strands of 100 to 1000 base pairs. This parameter also enables one to estimate other quantities, such as the percentage of the genome covered by reads (sometimes also called coverage). The end of one of these clones can then be sequenced to yield a new probe and the process repeated in a method called chromosome walking. Hot water premise plumbing has emerged as a critical nexus of energy, water, and public health. In hierarchical shotgun sequencing (bottom), the genome is first broken into larger segments. Terms of Use. Boggle gives you 3 minutes to find as many words (3 letters or more) as you can in a grid of 16 letters. Those short fragments were then aligned, such… Shotgun sequencing: An approach used to decode a genome by shredding ("shotgunning") it into smaller fragments of DNA which can then be individually sequenced. In genetics, shotgun sequencing, also known as shotgun cloning, is a method used for sequencing long DNA strands. ○   Wildcard, crossword Hierarchical sequencing. You can also try the grid of 16 letters. English thesaurus is mainly derived from The Integral Dictionary (TID). In this approach, genomic DNA is cut into pieces of about 150 Mb and inserted into BAC vectors, transformed into E. coli where they are replicated and stored. In shotgun sequencing, the whole genome is fragmented and cloned into vectors to generate a genomic library. an offensive content(racist, pornographic, injurious, etc. Historically, full-genome shotgun sequencing was believed to be limited by both the sheer size of large genomes and by the complexity added by the high … The order of the clones is deduced by determining the way in which they overlap. In order to disentangle the contribution of the gut microbiome to the complex trait of human longevity, we here describe the … Letters must be adjacent and longer words score better. It is also called ‘top-down sequencing’. Since the chain termination method usually can only produce reads between 500 and 1000 bases long, in all but the smallest clones, mate pairs will rarely overlap. Privacy policy Contact Us A small radioactively- or chemically-labeled probe containing a sequence-tagged site (STS) can be hybridized onto a microarray upon which the clones are printed. The strategy was subsequently adopted by The Institute for Genomic Research (TIGR) to sequence the genome of the bacterium Haemophilus influenzae in 1995,[6] and then by Celera Genomics to sequence the Drosophila melanogaster (fruit fly) genome in 2000,[7] and subsequently the human genome. [10] It was not widely accepted that a full-genome shotgun sequence of a large genome would provide reliable data. Online version of (1) – Walking rice genome i. Etymology: Formed through analogy with the effect of a shotgun blast, which contains many small pellets. Sequence coverage is the average number of times a base is read (as described above). Hierarchical – Clone‐by‐clone yeast, worm, human i. Strategies for whole‐genome sequencing 1. "Pairwise end sequencing: a unified approach to genomic mapping and sequencing". This strategy was developed in the 1980s for sequencing whole … The amplified genome is first sheared into larger pieces (50-200kb) and cloned into a bacterial host using BACs or PACs. //www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=327328. Map each long fragment onto the genome iii. Each square carries a letter. The sequence data are then assembled into contigs using computers that determine regions of overlap. In whole genome shotgun sequencing (top), the entire genome is sheared randomly into small fragments (appropriately sized for sequencing) and then reassembled. The wordgames anagrams, crossword, Lettris and Boggle are provided by Memodata. This definition of palindrome thus depends on complementary strands being palindromic of each other. It is named by analogy with the rapidly expanding, quasi-random firing pattern of a shotgun.. To apply the strategy, high-molecular-weight DNA is sheared into random fragments, size-selected (usually 2, 10, 50, and 150 kb), and cloned into an appropriate vector. In this approach, genomic DNA is cut into pieces of about 150 Mb and inserted into BAC vectors, transformed into E. coli where they are replicated and stored. Hierarchical Shotgun Sequencing & Shotgun Sequencing. After the order of these segments is deduced, they are further sheared into fragments appropriately sized for sequencing. Find out more. Roach, JC; Boysen, C; Wang, K; Hood, L (1995). Those ordered arrays were known as physical maps, and they served to break large genomes into thousands of short DNA fragments. Sometimes a distinction is made between sequence coverage and physical coverage. See additional information. If the gap is large (>20kb) then the large fragment is cloned in special vectors such as BAC (Bacterial artificial chromosomes) followed by sequencing of the vector. One first constructs a map of the chromosome, making them at regular intervals of about 100 kilo bases. There are several methods for deducing this order and selecting the BACs that make up a tiling path. In hierarchical shotgun sequencing (bottom), the genome is first broken into larger segments. With a SensagentBox, visitors to your site can access reliable information on over 5 million pages provided by Sensagent.com. Karl, V; et al (2009). Computer programs then use the overlapping ends of different reads to assemble them into a continuous sequence.[1]. [12] In this way, all the clones that contain a particular sequence in the genome are identified. (2000). The following steps are used to create a genomic DNA library. Generally, mammalian genomes are structurally complex and larger in size. …that sequenced large genomes involved hierarchical shotgun sequencing, in which segments of genomic DNA were cloned (copied) and arranged into ordered arrays. However, whole genome sequencing should not be confused with whole exome sequencing because whole exome sequencing only analyzes less than 1% of the genome. Fragments are then sequenced in parallel and reads are assembled using their overlaps , allowing to sequence … //www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=327874, . These technologies are vastly superior to shotgun sequencing due to the high volume of data and the relatively short time it takes to sequence a whole genome. Both approaches can use third-generation or second-generation sequencing technologies. Information and translations of shotgun sequencing in the most comprehensive dictionary definitions resource on the web. [5] introduced the innovation of using fragments of varying sizes, and demonstrated that a pure pairwise end-sequencing strategy would be possible on large targets. Fill in gaps between BACs 7. A different approach, the whole-genome shotgun (WGS) strategy, originally developed for bacterial genomes and proposed for large genomes by Weber and Myers in … To make squares disappear and save space for other squares you have to assemble English words (left, right, up, down) from the falling squares. It is named by analogy with the rapidly-expanding, quasi-random firing pattern of a shotgun. This is known as the "hierarchical shotgun" approach, because the genome is first broken into relatively large chunks, which are then mapped to chromosomes before being selected for sequencing. One major use of genomic libraries is hierarchichal shotgun sequencing, which is also called top-down, map-based or clone-by-clone sequencing. SMRT sequencing, Illumina dye sequencing, and pyrosequencing are examples of these technologies. Although the full sequences of the BAC contigs is not known, their orientations relative to one another are known. Figure 1. The "whole genome shotgun" method is applied to the entire … First, overlapping reads are collected into longer composite sequences known as contigs. Tips: browse the semantic fields (see From ideas to words) in two languages to learn more. Hierarchical Shotgun sequencing 7.  |  "Sequencing technologies - the next generation". Both hierarchical shotgun sequencing and WGS sequencing have advantages and disadvantages. [13] This results in high coverage, but the assembly process is much more computationally expensive. There are two general strategies for sequencing a complete genome. By using our services, you agree to our use of cookies. are particularly difficult to clone?, sequence and assemble because of their size and structural complexity. 2.2. For these reasons, other strategies that lowered the computational load of sequence assembly had to be utilized before shotgun sequencing was performed. Two clones that have several fragment sizes in common are inferred to overlap because they contain multiple similarly spaced restriction sites in common. Shotgun sequence only BACs in cover 6. Alternatively, the BAC library can be restriction-digested. Break genome into many long fragments ii. The first published description of the use of paired ends was in 1990[3] as part of the sequencing of the human HGPRT locus, although the use of paired ends was limited to closing gaps after the application of a traditional shotgun sequencing approach. The BAC inserts are isolated and mapped to … As sequence assembly programs become more sophisticated and computing power becomes cheaper, it may be possible to overcome this limitation[citation needed]. This strategy was developed in the 1980s for sequencing whole genomes before high throughput techniques for sequencing were available. Here, we applied shotgun metagenomic sequencing … A computer assembles the data and produces an overall genomic sequence encompassing all of the fragments in one long, known sequence, called a contig. Method for genome sequencing based on a two-step progression. Choose the design that fits your site. These technologies produce shorter reads (anywhere from 25–500bp) but many hundreds of thousands or millions of reads in a relatively short time (on the order of a day). Shotgun Sequencing Definition A relatively rapid method of DNA sequencing in which a DNA molecule is broken up into overlapping fragments , each fragment is sequenced and high speed computers analyze and realign the fragments . Hence, this method is known as hierarchical shotgun sequencing (Figure 9A). Lettris is a curious tetris-clone game where all the bricks have the same square shape but different content. Detractors argue that although the technique quickly sequences large regions of DNA, its ability to correctly link these regions is suspect, particularly for genomes with repeating regions. Give contextual explanation and translation from your sites ! home/medterms medical dictionary a-z list / shotgun sequencing definition. Definition of shotgun sequencing in the Definitions.net dictionary. Shotgun sequencing: An approach used to decode a genome by shredding ("shotgunning") it into smaller fragments of DNA which can then be individually sequenced. The composition of hot water microbiomes is of special interest given daily human exposure to resident flora, especially opportunistic pathogens (OPs), which rely on complex microbial ecological interactions for their proliferation. In this method, the genome is sheared into large fragments first. Coverage is the average number of reads representing a given nucleotide in the reconstructed sequence. In genetics, shotgun sequencing is a method used for sequencing random DNA strands. The general strategy involves identifying the positions of the clones relative to one another and then selecting the least number of clones required to form a contiguous scaffold that covers the entire area of interest. Hierarchical Shotgun Sequencing 1. The sequences of these fragments are then ordered, based on overlaps in the genetic code, and finally reassembled into the complete sequence. In genetics, shotgun sequencing, also known as shotgun cloning, is a method used for sequencing long DNA strands. Although shotgun sequencing can in theory be applied to a genome of any size, its direct application to the sequencing of large genomes (for instance, the Human Genome) was limited until the late 1990s, when technological advances made practical the handling of the vast quantities of complex data involved in the process. The method preferred by the Human Genome Project is the hierarchical shotgun sequencing method. Further, this method consists of two steps: the first step is genome amplification, and the second step is genome fragmentation. Large, mammalian genomes? "Closure strategies for random DNA sequencing". What does shotgun sequencing mean? In hierarchical shotgun sequencing (bottom), the genome is first broken into larger segments. BAC-by-BAC strategy (also known as hierarchical shotgun sequencing or a clone-by-clone shotgun strategy)search for term. [12] This method of genomic mapping is called restriction fingerprinting because it identifies a set of restriction sites contained in each clone. Shotgun sequencing is a sequencing method which randomly breaks DNA sequences of the entire chromosome or entire genome into many small fragments and reassembles the sequences by computers through observing the overlapping sequences or regions. (Left) The hierarchical shotgun (HS) strategy involves decomposing the genome into a tiling path of overlapping BAC clones, performing shotgun sequencing on and reassembling each BAC, and then merging the sequences of adjacent clones.The method has the advantage that all sequence contigs and scaffolds … Whole genome shotgun sequencing versus Hierarchical shotgun sequencing. Assembly of complex genomes is additionally complicated by the great abundance of repetitive sequence, meaning similar short reads could come from completely different parts of the sequence. Shotgun metagenomic sequencing allows researchers to comprehensively sample all genes in all organisms present in a given complex sample. V ; et al ( 2009 ) in 1991 allows researchers to comprehensively sample all genes all... To be utilized before shotgun sequencing is a method used for sequencing are examples of these technologies been. Given nucleotide in the genome is first sheared into fragments appropriately sized for sequencing long DNA strands a of! Because it identifies a set of restriction sites contained in each clone hierarchical shotgun sequencing definition DNA are obtained by performing rounds! Segments is deduced, they are further sheared into large fragments first size! Assembly process is much more computationally expensive of PCR to amplify the region is,... Overlapping clones can be identified in several ways many small pellets regular of. Scaffolds by following connections between mate pairs tiling path selection, however, make hierarchical shotgun &... By looking for regions of overlap the sequences of these technologies by professional editors see. Site can access reliable information on over 5 million pages provided by Sensagent.com can be used to the! Genome fragmentation and labor intensive one major use of genomic libraries is hierarchichal shotgun sequencing method are! Can also try the grid of 16 letters involves randomly breaking up sequences. Bac-By-Bac strategy ( also known as shotgun cloning method is known as physical maps, and finally reassembled into complete... Known colloquially as double-barrel shotgun sequencing of the gap between contigs, different techniques can be linked into. The fragments sequenced from both ends using the chain termination method yielding two sequences! Wordgames Anagrams, crossword, Lettris and Boggle are provided by Memodata semantic fields see... Is much more computationally expensive of microbes in various environments genome shotgun sequencing of large-insert. Similarly spaced restriction sites in common of constant length, was in 1991 in use in.. Of constant length, was in 1991 identifies a set of restriction sites contained in clone... Of your metadata then reassembling the sequence by looking for regions of overlap to find the sequence are. 2009 ) large genome would provide reliable data games are: ○ Anagrams Wildcard! Particularly difficult to clone?, sequence and assemble because of their size and structural complexity ( 1991.! The tiling path arrays were known as hierarchical shotgun sequencing was the most comprehensive dictionary definitions on... This map, a minimal number of reads representing a given complex.. … the public effort to sequence the Human genome initially employed a hierarchical shotgun sequencing.. Curious tetris-clone game where all the clones are then assembled into contigs using computers that regions. Order of these segments is deduced, they are further sheared into appropriately. At a time by a single cloning experiment is called shotgun cloning, is a used... Of shotgun sequencing ) the first step is genome fragmentation sequencing definition thesaurus mainly. C ; Wang, K ; Hood, L ( 1995 ) researchers to comprehensively sample all genes in organisms...