single nucleotide polymorphism (SNP)« Back to Glossary Index
A single nucleotide polymorphism (SNP) is a DNA variation in which one nucleotide (the building block of DNA) differs from what is generally observed in the population. SNPs occur normally throughout a person’s DNA — usually about once in every 300 nucleotides. These variations are typically found in the DNA between genes. They can act as markers, helping scientists locate genes that are associated with a specific disease. When SNPs appear within a gene or in a regulatory region near a gene, they may play a more direct role in disease by affecting the function of a gene.