What Is a SNP (Single Nucleotide Polymorphism)?

A SNP, pronounced “snip,” is the most common type of genetic variation, occurring when a single nucleotide (A, T, G, or C) differs between individuals at a specific position in the DNA sequence. On average, SNPs occur roughly once in every 300 nucleotides, meaning there are millions of SNPs across the human genome.

Most SNPs have no direct effect on health, but some are associated with disease risk, drug response, or physical traits, making them a key focus of genetic research and many DNA tests.

References: medlineplus.gov/genetics; genome.gov