DNA sequencing is the process of determining the precise order of nucleotides within a DNA molecule.It includes any method or technology that is used to determine the order of the four bases— adenine, guanine, cytosine, and thymine —in a strand of DNA.The advent of rapid DNA sequencing methods has greatly accelerated biological and medical research and discovery.NA sequencing is the determination of the physical order of these bases in a molecule of DNA. However, there are many other bases that may be present in a molecule. In some viruses (specifically, bacteriophage), cytosine may be replaced by hydroxy methyl or hydroxy methyl glucose cytosine.