20th February 2024

DNA sequencing

DNA sequencing determines the precise sequence of A, C, T and G nucleotides within the gene of interest. It is helpful in detecting insertion, deletion, point mutations and nucleotide polymorphisms. At its core, sequencing is performed using either the Sanger method or next-generation sequencing (NGS).

The Sanger method analyses a DNA sequence by starting with multiple DNA strands and a primer to target a sequence of interest. Dideoxynucleoside molecules terminate the nucleotide chain during the reaction, creating multiple chains of DNA with differing lengths. Each dideoxynucleoside is attached to its fluorescent dye, and a computer program compares each fragment’s size and the fluorescent dye present to determine the precise DNA sequence. This process is labour-intensive but allows a specific gene to be sequenced accurately.

NGS allows rapid sequencing of an entire genome. The genome is divided into millions of fragments, each up to several hundred base pairs in size. Fragments are amplified using PCR, complementary base pairs are attached, and laser scanning helps to identify the fluorescent dye. It is useful to detect rare genetic diseases caused by mutations of various genes.