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SNP
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<p><font size="3">SNPs could be bi-, tri-, or tetra-allelic polymorphisms. <br />However, in humans, tri-allelic and tetra-allelic SNPs are rare almost <br />to the point of non-existence, and so SNPs are sometimes simply <br />referred to as bi-allelic markers (or di-allelic) </font></p>
<p><font size="3">The typical frequency with which one observes single base differences in genomic <br />DNA from two equivalent chromosomes is of the order of 1/1000 bp = 0.1% </font></p>
<p><font size="3">cf) non-coding HLA regions show nucleotide diversity levels of 5–10% <br /><br /></font><font size="3"><strong>[Application]<br /></strong><br /><em>Population genetics and linkage disequilibrium </em> :<br />The study of the genetic composition and inter-relationships between <br />populations. The major research tool it uses is DNA polymorphism. </font></p><p><font size="3"><em>Complex phenotypes and genome variation :<br /></em>Risks of major common diseases such as cancer, cardiovascular disease, <br />mental illness, auto-immune states, and diabetes, are expected to be heavily<br />influenced by the patterns of SNPs one possesses in certain key susceptibility <br />genes yet to be identified. </font></p><p><font size="3"><em>SNP based association studies :</em><br />If a factor contributes an increased risk for disease occurrence, then that factor <br />should be found at higher frequency in individuals with that disease compared to <br />non-diseased controls </font></p>
<p><font size="3"><strong>[Reference]</strong><br />Brookes AJ, The essence of SNPs, Gene. 1999 Jul 8;234(2):177-86.<br /></font><br /></p>