Editing Single-nucleotide polymorphism (section)

=== Within a genome ===
The genomic distribution of SNPs is not homogenous; SNPs occur in [[Noncoding DNA|non-coding regions]] more frequently than in [[coding region]]s or, in general, where natural selection is acting and "fixing" the [[allele]] (eliminating other variants) of the SNP that constitutes the most favorable genetic adaptation.<ref name="Barreiro">{{cite journal | vauthors = Barreiro LB, Laval G, Quach H, Patin E, Quintana-Murci L | s2cid = 205357396 | title = Natural selection has driven population differentiation in modern humans | journal = Nature Genetics | volume = 40 | issue = 3 | pages = 340–5 | date = March 2008 | pmid = 18246066 | doi = 10.1038/ng.78 }}</ref> Other factors, like [[genetic recombination]] and mutation rate, can also determine SNP density.<ref name="Nachman">{{cite journal | vauthors = Nachman MW | title = Single nucleotide polymorphisms and recombination rate in humans | journal = Trends in Genetics | volume = 17 | issue = 9 | pages = 481–5 | date = September 2001 | pmid = 11525814 | doi = 10.1016/S0168-9525(01)02409-X }}</ref>

SNP density can be predicted by the presence of [[Microsatellite (genetics)|microsatellites]]: AT microsatellites in particular are potent predictors of SNP density, with long (AT)(n) repeat tracts tending to be found in regions of significantly reduced SNP density and low [[GC content]].<ref name="Varela">{{cite journal | vauthors = Varela MA, Amos W | title = Heterogeneous distribution of SNPs in the human genome: microsatellites as predictors of nucleotide diversity and divergence | journal = Genomics | volume = 95 | issue = 3 | pages = 151–9 | date = March 2010 | pmid = 20026267 | doi = 10.1016/j.ygeno.2009.12.003 | doi-access =  }}</ref>