Tuesday, 14 April 2020

The whole-genome sequencing

whole-genome sequencing


Development of molecular biology DNA whole-genome sequence is the basis pair of highly automated and useful for DNA analysis sequencingThe ultimate physical map is the base-pair sequence of an entire genome. In the early days of molecular biology, all sequencing was done manually, and was, therefore, both time- and labor-intensive the development of machines to automate this process increased the rate of sequence generation.

On a larger scale, it is useful for high-automated computer analysis and sequencing for genome sequencing. One such genome sequencing, which baffles technology science, in a few hours, an automated Sanger sequencer can sequence the same number of base-pairs that a technician can manually sequence up to 50,000 bp a year. With the current generation of sequencing technology described in the previous chapter, the rate of sequence generation is now five orders of magnitude greater than when the human genome was sequenced with automated Sanger sequencers. 

Genome sequencing requires larger molecular clones

To isolate DNA from an organism, it would be ideal to add in a sequencer, then in a week or two to take a computer-generated printout of the genome sequence, a process that is not straightforward. Sequencers for DNA segments provide precise sequences of up to 800 bp. However, errors are possible. To reduce errors, each causal clone can be sequenced 5–10 times.


Artificial chromosomes

The development of artificial chromosomes of DNA has allowed scientists to clone large fragments. The first generation of these new vectors were yeast artificial chromosomes (YACs). The centromere sequence and they are constructed using the origin of replication, then foreign DNA is added to it. The origin of this replication is allowed to replicate independently of the rest of the artificial chromosome genome, and the centromere sequences make the chromosome stable.

YACs are used to clone large pieces of DNA, they had several drawbacks, including the tendency to rearrange portions of DNA by deletion. Despite these difficulties, YAC was used for physiological construction by restriction enzyme digestion of YAC DNA.

Artificial chromosomes are most commonly used in E-coli, especially for large-scale sequencing. These bacterial synthetic chromosomes (BACs) accept bacterial DNA plasmid BAC vectors between 100 and 200 km of DNA inserts. The downside of BAC vectors is that, like chromosomes, bacteria are kept as one copy while plasmid vectors are present in high copy numbers.


Human artificial chromosomes

Human DNA can present in cells from large areas of the human artificial chromosome. These artificial chromosomes are usually constructed by fragmentation of chromosomes with centromere sequences. Some circulars may still separate correctly during mitosis up to 98% of the time. The construction of linear human artificial chromosomes is not yet possible.

Whole-genome sequencing is approached in two ways: clone-by-clone and shotgun

Sequencing an entire genome is an enormous task. Two ways of approaching this challenge have been developed: one that approaches the sequencing one step at a time, and another that attempts to take on the whole thing at once and depends on computers to sort out the data. The two techniques grew out of competing projects to sequence the human genome.

Clone-by-clone sequencing

The cloning of large inserts in BACs facilitates the analysis of entire genomes. Creating a physical map, and then a strategy commonly adopted for subsequent sequencing is used to place the site of the first BAC clones.

Clone-by-clone sequencing

Figure. The clone-by-clone method uses large clones assembled into overlapping regions by STSs. Once assembled, these can be fragmented into smaller clones for sequencing.

To align a large part of the chromosome it is necessary to identify regions that overlap between clones. This can be accomplished by constructing each BAC clone either a restriction map or identifying STs found in the clone. If the two STs in the BAC clone are identical, it will be necessary to overlap them.

Alignment of a number of BAC clones Accidentally there is a sudden stretch of DNA. personally, BAC clones can be assigned to a sequence of 500 bp at a time that the entire comb sequence can be formed. The latter sequencing is called physical clone-by-clone sequencing.

Shotgun sequencing

The idea of shotgun sequencing is simply to randomly cut the DNA into small fragments, sequence all cloned fragments, and then use a computer to put together the overlaps. This actually occurs in the early days of molecular cloning when the creation of a library of fragmented fragments was called shotgun cloning. This approach is much less compared to the clone-by-clone method but requires much more computer power to assemble the final sequence and be a very efficient algorithm for finding overlap.

Shotgun sequencing

Figure. In the shotgun method, the entire genome is fragmented into small clones and sequenced. Computer algorithms assemble the final DNA sequence based on overlapping nucleotide sequences.

Shotgun sequencing does not tie the sequence to any other information about the genome, unlike the clone-by-clone approach. Many investigators have used both clone-by-clone and shotgun-sequencing techniques, a hybrid approach that builds the strength to bind sequences to a physical map in this combination, while greatly reducing the time involved.

An assembler program that compares multiple copies of indexed regions to assemble a sequence, but one sequence that matches all copies. Because computer assemblers are incredibly powerful, the ultimate requirement for the human analysis is to determine after both shotgun sequencing and clone-by-clone when a genome sequence is sufficient to be useful to researchers.

The Human Genome Project used both sequencing methods


Initiated a new way of conducting biological research involving large teams of genomics on a large scale. But a single individual can isolate and manually sequence molecular clones for a single gene, a collaborative effort by researchers from hundreds of large genomes, such as the human genome.

The Human Genome Project began in 1990 by a group of American scientists when the International Human Genome Sequencing Consortium was formed. Funded were publicly using a clone-by-clone approach to target sequences of the human genome. Sequences of each chromosome were used as physical and genetic maps.

In May 1998, Craig Venter, whose research group had sequenced Haemophilus influenza, announced his private company (Celera Genomics) would sequence the human genome. In two years he proposed only the 3.2-gigabyte genome shotgun-sequence. The association raced to challenge and introduce human genome sequencing. In contrast, there was a tie. On 26 June 2000, the groups jointly declared success, and all published their findings together in 2001.

The association consisted of 248 authors. The sequence of the human genome was still early. Gaps are being filled in the sequence, and the map is constantly being refined. The "finished" human sequence is 400-fold deficient by only 260 intervals, and now includes 99% of euchromatic sequences, with an error rate of 100,000 references per sequence in terms of 95%. New sequencing techniques are being used to shut down. Remaining interval. A few individuals, including James Watson who co-discovered the structure of DNA, have now had their personal genomes sequenced. The cost of having one’s genome sequenced is predicted to fall to $1000 in the next few years, raising many questions about genome privacy.

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