Single Nucleotide Polymorphism

The term is often shortened to SNP and pronounced as a word. At a particular genomic position, people may carry different DNA letters. A person inherits one copy of most autosomal positions from each parent, so a report may describe zero, one, or two copies of a particular allele.

Most individual SNPs do not have a simple standalone meaning. Some are located within genes, some help regulate activity, and many sit between coding regions. A SNP can also act as a marker inherited near another variant. Association does not automatically explain mechanism or determine an individual outcome.

Genotyping arrays test a defined selection of positions, whereas sequencing can examine broader regions and identify other variant types. Strand orientation, genome build, allele naming, assay coverage, and quality control matter when comparing reports. Pharmacogenomic and broader genomic interpretations may use SNPs, but their conclusions depend on evidence beyond the presence of one letter.

SNP identifiers often begin with the letters rs followed by numbers. That identifier points to a database record, not to one fixed interpretation. The same position can be discussed using different reference strands, so the reported allele needs orientation and genome context.

Nearby variants can be inherited together through linkage disequilibrium. This allows one SNP to act as a statistical marker for a surrounding genomic region, but it does not mean that the marker itself is necessarily the functional variant responsible for an association.

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