Sequencing the human genome was an enormous project costing a great deal but fully sequencing the entire DNA series. Since that accomplishment, the technology has continued to improve for sequencing.
To map the sequence quickly and cheaply, the best approach might be “nanopore sequencing,” in which individual strands of DNA are drawn through tiny holes and the base pairs simultaneously “read” for the sequence. At present, DNA has to be copied millions of times, given fluorescent tags as preparation, which takes five to ten days – steps that can be skipped if nanopore sequencing is used instead.
Current methods chop up DNA into sequences of 100 base pairs, which have to be sequences multiple times for errors and consistency. Nanopore sequencing allows for much longer pairs to be processed.
Copying what ion channels accomplish in cell membranes, exonuclease sequencing already exists to achieve this process. But a problem is that as many as fifteen base pairs are in the nanopore at one time, allowing for possible errors. The speed with which the sequence goes through the pore must be carefully controlled to insure that the base pairs are accurately and fully read.
By modifying the protein and creating a constriction in the nanopore, and by attaching a polymerase enzyme to the AHL protein (the material around which the nanopore is created), DNA can be ratcheted through the tiny hole base pair by base pair. With a lot of nanopores working in parallel, a gene could be sequenced fairly rapidly.
An alternative approach is to create artificial nanopores in solid state materials. IBM and a division of Roche pharmaceuticals have been working together to this end. By layering titanium nitrade with insulating layers of silica and using an electron microscope to punch nanoholes in the material, electrical charge can ratchet a DNA sequence through the material, base pair by pair. The poles can be reversed and the ratchet can operate backwards to catch errors. Others are working on solid state nanopores using graphene, a material consisting of a monolayer of carbon. With such thin material, only a single base will be present in the material at any time. A group at the University of Pennsylvania suggests adding a layer of titanium oxide to the graphene improves accuracy by reducing the noise level.
Rapid and complete sequencing would allow comparison of healthy and cancerous cells' DNA of a patient. It would be useful in determining which drugs would assist a particular patient the best. It would also allow for a thorough survey of human evolution and dispersion throughout the world.
– summarized by the blog author from: http://www.economist.com/node/18304268 (which also contains some useful graphics explaining the process)
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