In genetics, what is the name of a DNA variation involving a single nucleotide at a specific genome position?

In genetics, a DNA variation involving a single nucleotide at a specific genome position is called a single-nucleotide polymorphism, or SNP.

A SNP occurs when individuals in a population commonly differ at one DNA base position. For example, one person may carry an adenine at a site where another carries a guanine. A variant is generally described as a polymorphism when it is sufficiently common in a population, rather than being an extremely rare change.

Many SNPs have no noticeable effect because they occur outside protein-coding regions or do not alter the amino acid specified by a coding sequence. Other SNPs can influence gene regulation, protein structure, disease susceptibility, or responses to medicines.

Researchers use SNPs as genetic markers in association studies, ancestry analysis, and some forms of personalized medicine. A SNP is different from a copy-number variation, which changes the number of copies of a larger DNA segment.