the oldest DNA sequenced to date. Metagenomics The field of metagenomics involves identification of organisms present in a body of water, sewage, dirt, debris filtered from the air, or swab samples from organisms. Knowing which organisms are present in a particular environment is critical to research in ecology, epidemiology, microbiology, and other fields. Sequencing enables researchers to determine which types of microbes may be present in a microbiome, for example. Virology As most viruses are too small to be seen by a light microscope, sequencing is one of the main tools in virology to identify and study the virus. Viral genomes can be based in DNA or RNA. RNA viruses are more time-sensitive for genome sequencing, as they degrade faster in clinical samples. Traditional Sanger sequencing and next-generation sequencing are used to sequence viruses in basic and clinical research, as well as for the diagnosis of emerging viral infections, molecular epidemiology of viral pathogens, and drug-resistance testing. There are more than 2.3 million unique viral sequences in GenBank. Recently, NGS has surpassed traditional Sanger as the most popular approach for generating viral genomes. During the 1990 avian influenza outbreak, viral sequencing determined that the influenza sub-type originated through reassortment between quail and poultry. This led to legislation in Hong Kong that prohibited selling live quail and poultry together at market. Viral sequencing can also be used to estimate when a viral outbreak began by using a molecular clock technique. Medicine Medical technicians may sequence genes (or, theoretically, full genomes) from patients to determine if there is risk of genetic diseases. This is a form of genetic testing, though some genetic tests may not involve DNA sequencing. DNA sequencing is also being increasingly used to diagnose and treat rare diseases. As more and more genes are identified that cause rare genetic diseases, molecular diagnoses for patients becomes more mainstream. DNA sequencing allows clinicians to identify genetic diseases, improve disease management, provide reproductive counseling, and more effective therapies. Also, DNA sequencing may be useful for determining a specific bacteria, to allow for more precise antibiotics treatments, hereby reducing the risk of creating antimicrobial resistance in bacteria populations. Forensic investigation DNA sequencing may be used along with DNA profiling methods for forensic identification and paternity testing. DNA testing has evolved tremendously in the last few decades to ultimately link a DNA print to what is under investigation. The DNA patterns in fingerprint, saliva,