what is a genetic marker

A genetic marker is a DNA sequence with a known physical location on a chromosome that can be used to identify individuals or species. It can be described as a variation that can be observed, such as a change in a single nucleotide (single nucleotide polymorphism, SNP) or a longer sequence like minisatellites. Genetic markers can be used to track the inheritance of a nearby gene that has not yet been identified, but whose approximate location is known. They are also used to study the relationship between an inherited disease and its genetic cause. Genetic markers can be divided into two classes: biochemical markers which detect variation at the gene product level such as changes in proteins and amino acids, and molecular markers which detect variation at the DNA level such as nucleotide changes: deletion, duplication, inversion, and/or insertion. Markers can exhibit two modes of inheritance, i.e. dominant/recessive or co-dominant. There are many types of molecular genetic markers, including RFLP, SSR, AFLP, CAPS, dCAPS, STS, RAPD, and SNP.