What is DNA sequencing?

DNA sequencing is any process used to map out the sequence of the nucleotides that comprise a strand of DNA.  Each cell in an organism contains the genetic code for the entire organism. The process of DNA sequencing transforms the DNA from a given organism into a format that can be used by researcheArs for the basic study of biologic processes, medical research, and in forensics.

There are two main methods of DNA sequencing:

1. Sanger dideoxy (primer extension/chain-termination) method: most popular protocol for sequencing, very daptable, scalable to large sequencing projects
2. Maxam-Gilbert chemical cleavage method: DNA is labelled and then chemically cleaved in a sequence dependent manner. This method is not easily scaled and is rather tedious.

Modern sequencing equipment uses the principles of the Sanger technique.

DNA sequencing applications

DNA sequencing may be used to determine the sequence of individual genes, larger genetic regions (i.e. clusters of genes or operons), full chromosomes or entire genomes. Depending on the methods used, sequencing may provide the order of nucleotides in DNA or RNA isolated from cells of animals, plants, bacteria, archaea, or virtually any other source of genetic information. The resulting sequences may be used by researchers in molecular biology or genetics to further scientific progress or may be used by medical personnel to make treatment decisions or aid in genetic counseling.

In medicine:

DNA sequencing of the human genome project has helped in identification of several genes associated with genetic conditions, including familial breast cancer and colorectal cancer, Alzheimer's disease, myotonic dystrophy, neurofibromatosis and fragile X syndrome. It helps in better diagnosis of diseases and will become a part of a patient's medical record, helping physicians to determine the patient's risk of certain diseases and the optimal treatments.

In Forensic:

It helps in DNA fingerprinting i.e. identification of criminal from the proofs available from the crime scene. It also helps in identification of the paternity of a child.

In Agriculture:

It helps in identification of genes of crop and facilitates improvement of crop which can have high yields, pest tolerance, etc.

The applications of next-generation sequencing technologies are vast, owing to their relatively low cost and large-scale high-throughput capacity. Using these technologies, scientists have been able to rapidly sequence entire genomes (whole genome sequencing) of organisms, to discover genes involved in disease, and to better understand genomic structure and diversity among species generally.