In virology, sequencing is one of the main tools to identify and study viruses, since most viruses are too small to be seen with a light microscope. Sequencing of viruses in basic and clinical research, molecular epidemiology of viral pathogens, and drug resistance testing using conventional Sanger sequencing and next-generation sequencing (NGS) are all performed using these methods. The GenBank database contains more than 2.3 million unique viral sequences. Non-directed genome sequencing has recently gained popularity over traditional Sanger sequencing as the primary method for generating viral genomes. Download the free pdf study notes from Vedantu.com.