Genetic marker

A genetic marker is a specific discovered single nucleotide polymorphism or SNP (or simply "mutation") of certain section of DNA of a specific genome. The SNP can either be associated with a known genetic disease, or, it can be in junk DNA that occurs in many individuals and thus be useful for population studies. For the later case, such a mutation would have had to have originated many of hundreds of generations previously and become widespread. Another kind of genetic marker would be a counted short tandem repeats (STRs), where the exact counts are generally inherited.

Genetic markers are used in the studies of populations, such as studies of the migrations of peoples. In particular, genetic markers associated with the Y-chromosome persist along paternal lines and the genetic markers identified in mitochondrial DNA persist along maternal lines. Note that the Y-chromosome has about 25 million base pairs where mitochondrial DNA has about 16 thousand. This persistence is due to the fact that the Y-chromosome in male offspring and the mitochondria in all offspring are clones of the corresponding parent. Note that these SNP's are often in a region of junk DNA and so have no known impact on expressed genetic traits and no implications for biological function.

STRs on the Y-chromosome are also widely used and are known as DNA Y-chromosome Segment (DYS). They necessarily fall in the category of junk DNA.

A paternal example of a genetic marker would be the M343 marker. This mutation would have originated in a Y chromosome replication in a cell of an individual male and then ended up in at least one of his sperm cells which subsequently achieved fertilization in his mate and live birth of a male offspring