Gene sequencing is a process in which the individual base nucleotides in an organism's DNA are identified. This technique is used to learn more about the genome of the organism as a whole, and to identify specific areas of interest and concern. A number of different techniques can be used, including BAC to BAC sequencing, which creates a map of the genome, and shotgun sequencing, which splices together multiple tiny fragments of the genome to get a total picture.
As soon as DNA was identified and its role was understood, researchers started sequencing it, because they were interested in the construction of the genome. Sequencing first successfully occurred with RNA, and later DNA. Biological samples like hair, skin scrapings, and blood can all be used. As long as a few cells are present, it's possible to extract their DNA and run it through a sequencer.
In DNA sequencing, the sample is tested to determine the order of the nucleotides. Researchers have been able to uncover specific genes that code for a variety of traits, from congenital heart conditions to brown hair. By looking at genetic variations across multiple individuals, researchers can identify the precise nucleotides used to code specific traits, and they can sometimes learn more about when the trait first appeared in the organism, and what kinds of factors can influence that trait.
Medical researchers are very interested in gene sequencing because the process can be used to identify genetic abnormalities. Researchers are also optimistic that the technique may someday lead to cures for specific conditions, along with additional general knowledge about the genomes of humans and other animals that could be useful. It's used today to test samples of material from fetuses to check for common genetic conditions and from parents who are concerned about passing down hereditary diseases.
In addition to being of interest to the medical field, gene sequencing interests scientists, because it allows them to set up a genetic clock to see when various traits emerged. This information can also be used to predict when an organism first appeared on Earth, and what it looked like at various points in its evolutionary lifetime. Criminologists also use DNA testing in their work, using common markers to test unknown samples against known DNA to see if someone was present at the scene of a crime.