Single-nucleotide polymorphism

A single-nucleotide polymorphism (SNP) is a genomic position where individuals commonly carry different nucleotides. SNPs are widespread genetic variants used to study inheritance, traits, and populations.

Nucleotide: A nucleotide is a DNA or RNA building block composed of a sugar, phosphate group, and nitrogenous base. A SNP changes which nucleotide occupies one genomic position.
DNA replication: DNA replication is the cellular process that copies a DNA molecule before cell division. Replication can introduce base substitutions that later become SNPs.
Genome-wide association study: A genome-wide association study tests many genetic variants across a population for statistical association with a trait or disease. SNPs are the usual markers tested to locate trait-associated genomic regions.
Single-nucleotide variant: A single-nucleotide variant is a DNA sequence difference at one nucleotide position, regardless of how common it is. SNP conventionally denotes a common variant, while this term includes rare substitutions.
Linkage disequilibrium: Linkage disequilibrium is the nonrandom association of alleles at different loci in a population. Correlated SNPs can mark a causal variant they are inherited alongside.
Allele: An allele is one of the alternative DNA sequences found at a particular genetic locus. Different nucleotides at a SNP define alternative alleles.
DNA polymerase: DNA polymerases are enzymes that synthesize DNA using an existing strand as a template. Polymerase errors can insert a wrong nucleotide during DNA copying.
Genetic linkage: Genetic linkage is the tendency of nearby loci to be inherited together because recombination rarely separates them. SNP linkage patterns help map nearby genes and variants.
Indel: An indel is an insertion or deletion of one or more DNA bases relative to a reference sequence. Indels alter sequence length, unlike a SNP's single-base substitution.
Population genetics: Population genetics studies genetic variation within and between populations and how it changes over time. SNP frequencies track population history, migration, and genetic drift.

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