brifely describe 2 methods used by DNA sequencing
1) Sanger sequencing: This method, also known as dideoxy sequencing or chain termination sequencing, was first developed by Frederick Sanger in 1977. It involves using DNA polymerase to synthesize new DNA strands in a reaction mixture containing a small amount of dideoxynucleotides, which lack a 3' hydroxyl group necessary for further DNA strand elongation. The reaction produces a set of DNA fragments of different lengths, each terminating with a specific nucleotide. These fragments are separated using gel electrophoresis based on their length, and their sequence can be deduced by reading the size of the separated fragments from smallest to largest.
2) Next-generation sequencing (NGS): This is a more recent method that revolutionized the field of DNA sequencing. It encompasses a range of high-throughput sequencing technologies, including pyrosequencing, Illumina sequencing, and Ion Torrent sequencing, among others. NGS methods involve massively parallel sequencing of millions of DNA fragments simultaneously. In general, the DNA sample is fragmented into small pieces, attached to adapters that enable clonal amplification, and then amplified through various methods. These amplified fragments are sequenced in parallel using nucleotide incorporation and detection techniques, with each nucleotide incorporation emitting a fluorescence or light signal that can be detected and recorded by a computer. The sequences of these millions of fragments are then aligned and assembled to reconstruct the original DNA sequence. NGS allows for rapid and cost-effective sequencing of large genomes and is widely used in various fields, including genomics, transcriptomics, and metagenomics.