DNA sequencer - AbsoluteAstronomy.com

A DNA sequencer is a scientific instrument

Scientific instrument

A scientific instrument can be any type of equipment, machine, apparatus or device as is specifically designed, constructed and often, through trial and error, ingeniously refined to apply utmost efficiency in the utilization of well proven physical principle, relationship or technology to...

used to automate the DNA sequencing

DNA sequencing

DNA sequencing includes several methods and technologies that are used for determining the order of the nucleotide bases—adenine, guanine, cytosine, and thymine—in a molecule of DNA....

process. It can be also considered an optical instrument

Optical instrument

An optical instrument either processes light waves to enhance an image for viewing, or analyzes light waves to determine one of a number of characteristic properties.-Image enhancement:...

as it generally analyses light signals originating from fluorochromes attached to nucleotides.

DNA sequencers have become more important due to large genomics

Genomics

Genomics is a discipline in genetics concerning the study of the genomes of organisms. The field includes intensive efforts to determine the entire DNA sequence of organisms and fine-scale genetic mapping efforts. The field also includes studies of intragenomic phenomena such as heterosis,...

projects and the need to increase productivity.

Modern automated DNA sequencing instruments (called DNA sequencers) are able to sequence multiple samples in a batch (run) and perform as many as 24 runs a day. These perform only the size separation and peak reading; the actual sequencing reaction(s), cleanup and resuspension in a suitable buffer must be performed separately.

The magnitude of the fluorescent signal is related to the number of strands of DNA that are in the reaction. If the initial amount of DNA is small, the signals will be weak. However, the properties of PCR allow one to increase the signal by increasing the number of cycles in the PCR program.

A simple DNA sequencer will have one or more lasers that emit at a wavelength that is absorbed by the fluorescent dye that has been attached to the DNA strand of interest. It will then have one or more optical detectors that can detect at the wavelength that the dye fluoresces at. The presence or absence of a strand of DNA is then detected by monitoring the output of the detector. Since shorter strands of DNA move through the gel matrix faster they are detected sooner and there is then a direct correlation between length of DNA strand and time at the detector. This relationship is then used to determine the actual DNA sequence.

The output of these machines is not perfect as it may contain reading errors and needs to be processed (see Sequence assembly

Sequence assembly

In bioinformatics, sequence assembly refers to aligning and merging fragments of a much longer DNA sequence in order to reconstruct the original sequence. This is needed as DNA sequencing technology cannot read whole genomes in one go, but rather reads small pieces of between 20 and 1000 bases,...

). Until a few years ago, this task was done manually by an operator. The assembly process for a contig made of 10 samples took about 5–15 minutes, depending on the quality of the samples. However, today, modern software can automatically process the output in seconds.

See also