The genetic information of living organisms (humans, animals, plants, fungi and some microorganisms) is contained within the genes, which are organized in DNA molecules (constituted by a desoxiribose sugar, a phosphate group and a nitrogenate base). This genetic information is different for each species and unique for each individual. The sequential order that the nitrogenate bases (adenine, thymine, cytosine and guanine) take will determinate the codification of different proteins, genes and therefore the individuals genetic and phenotypic characteristics.

DNA sequencing means deciphering the order that the nitrogenate bases follow and the genetic content of DNA fragments. This technology is of extraordinary interest due to the fact the results are wonderful informative tools benefiting areas of research on biological processes and fields applied to diagnosis, forensic medicine, an others. In the last few years several methods have been developed for DNA sequencing, and thanks to these many complete genetic sequences of living organisms have become known. The most used DNA sequencing method is the Dideoxy or Sanger`s Method (named after its inventor Frederick Sanger).

As a general idea, this process of DNA sequencing consists of the use of concentrated solutions of one strand DNA that needs to be sequenced that has been previously isolated and cloned in appropriated vectors through other biomolecular methods performed in the laboratory. Many copies of this DNA strand are then added to microtubes, joining it to a mix solution of previously optimized amounts of the four deoxy nucleotides, which are also labeled with fluorescent colour reagents (red, blue, yellow and green). Then a primer complementary to a sequence of the used vector and finally an enzyme called DNA polymerase are also added. This enzyme releases the beginning of the DNA pattern replication from the initial primer, incorporating the nitrogenate bases according to the rule of complementary (Adenine – Thymine and Cytosine – Guanine). After the replication of DNA molecules that are going to be sequenced, the next step is the reading of the DNA sequence. This can be conveniently produced through electrophoresis in polyacrilamyde gels and the use of nitrigenate bases with fluorescent colours. Also the reading can be made by an automatic process which requires essentially fluorochromos and generates a computer register of the fluorolabeled profile that represents the genetic sequence.

The development of a DNA sequencing methods has contributed to the impressive rate of new solutions to many mysteries in the biological processes. Its wide application around the world and the collaborative work between research groups has generated complete genetic sequences of certain animals, plants and microorganisms. Currently the huge Human Genome Project is also being worked on, so several and important results from these investigations are expected to be fundamental in the contribution and discovery of cures for major human diseases. Also the high demand for the procedure of DNA sequencing will lead to continued on work in this field of expertise to find the best method that could possibly produce millions of DNA sequences at the same time, at low costs and highly efficiency.