DNA sequencing is determining the order of nucleotides within sample of DNA, these nucleotides are adenine, guanine, cytosine, and thymine. Modern technology has allowed the sequencing of the entire human genome, this allows scientist to determine whether or not a person id predisposed to a genetic condition. Additionally, this allows for prescription medication to be tailor maid for a specific genome in a specific patient. DNA is can be sequenced through a method called Sanger sequencing, but this method is older and much simpler than next-generation sequencing. In Sanger sequencing, the DNA sample is combined within a tube with a primer, DNA polymerase, and DNA nucleotide with some that are dye labeled. This mixture is heated and cooled to denaturize the DNA sample, then the DNA primer and polymerase begin to sequence an additional strand, this continues until a dideoxy nucleotide is added. This process is repeated many times until the entire sample has been sequenced, then the sample runs through a process known as capillary gel electrophoresis. This process produces an image that can be read by scientists and enables then to be able to accurately determine the nucleotide sequence. Sanger sequencing was the original method of sequencing DNA but as technology has improved Next-generation sequencing has enabled scientist to sequence massive amounts of DNA. Next-generation sequencing is the term used for the most modern sequencing methods available, there are many next-generation methods but they all are all similar in their characteristics. In Next-generation sequencing many sequencing reactions occur at the same time, the reactions are on a micro scale very quickly and are extremely cost efficient. These reactions generally only sequence a section 50-700 nucleotide at a time, but since these reactions are highly parallel, a massive number of nucleotides can be sequences quickly

references:

https://www.khanacademy.org/science/biology/biotech-dna-technology/dna-sequencing-pcr-electrophoresis/a/dna-sequencing