A single nucleotide polymorphism (SNP) is a single DNA nucleotide that is polymorphic within a species. Each SNP has two alleles, represented by the nucleotide at that site (A,C,G or T). Some SNPs are in genes, and they can change the amino acid in the protein that the gene codes for, but most are in non-coding DNA.

SNPs can be identified in several different ways. Any mutation detection technique, such as denaturing gradient gel electrophoresis (DGGE) or denaturing high-performance liquid chromotography (DHPLC) can be used to identify sequence changes, which can be confirmed as polymorphic after observing that sequence change in DNA from several unrelated individuals. DHPLC was used to isolate SNPs on the human Y chromosome. Many SNPs in the human genome have been identified by comparison of clone sequence overlaps. If a certain sequence is covered by two or more...