<p>한개의 염기서열의 차이를 이용하는 것을 말한다.&nbsp;<br /><br />1번&nbsp;개체 AC<strong>C</strong>ATG<br />2번&nbsp;개체&nbsp;AC<strong>T</strong>ATG&nbsp;<br /><br />두&nbsp;개체간의 염기서열의 차이를 이용하게 된다.<br />예를 들어 특정 질병에&nbsp;잘 걸리는 집단과 잘 걸리지 않은 집단간의 유전자 차이를 비교, 질병의 원인을 규명혹은 마커 발견 할&nbsp;때 유용하게 쓰이게 된다.&nbsp;&nbsp;<br /><br /><font size="3"><strong><font size="4">[Definition]</font></strong><br />SNPs are single base pair positions in genomic DNA at which different <br />sequence alternatives (alleles) exist in normal individuals in some <br />population(s), wherein the <font color="#ff0000">least frequent allele </font> has an abundance <br />of <font color="#ff0000">1% or greater</font>.&nbsp;<br /></font></p><p><font size="3"><strong><br /><font size="4">[Narrow scope]</font></strong> <br />Single base insertion/deletion variants (indels) would not <br /><font color="#ff0000">formally </font> be considered to be SNPs.&nbsp;<br /></font></p><p><font size="3"><strong><br /><font size="4">[Pronunciation]</font></strong><br />SNP (pronounced 'S' 'N' 'P' or 'SNiP')&nbsp;<br /><br /><br /></font></p><p><font size="3"><strong><font size="4">[Characteristics of human SNPs]</font><br /></strong><br />Understand human <font color="#ff0000">DNA polymorphism, about 90% </font>of which is <br />single nucleotide polymorphism (SNP)&nbsp;<br /></font></p><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 <font color="#ff0000">bi-allelic markers </font> (or <font color="#ff0000">di-allelic</font>)&nbsp;<br /></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 <font color="#ff0000">1/1000&nbsp;bp = 0.1%</font>&nbsp;<br /></font></p><p><font size="3">cf) non-coding HLA regions show nucleotide diversity levels of 5&ndash;10%&nbsp;<br /><br /></font><font size="3"><strong><br /><font size="4">[Application]</font><br /></strong><br /><strong><em>Population genetics and linkage disequilibrium</em> :</strong><br />The study of the genetic composition and <font color="#ff0000">inter-relationships between <br />populations. </font> The major research tool it uses is DNA polymorphism.&nbsp;&nbsp;&nbsp;<br /></font></p><p><font size="3"><em><strong><br />Complex phenotypes and genome variation :</strong><br /></em><font color="#ff0000">Risks of major common diseases </font> such as cancer, cardiovascular disease, <br />mental illness, auto-immune states, and diabetes, are expected to be heavily<br />influenced by the patterns of <font color="#ff0000">SNPs one possesses in certain key susceptibility <br />genes yet to be identified.&nbsp;<br /></font></font></p><p><font size="3"><em><strong><br />SNP based association studies :</strong></em><br />If a factor contributes an increased risk for disease occurrence, <font color="#ff0000">then that factor <br />should be found at higher frequency in individuals with that disease </font> compared to <br />non-diseased controls </font></p><p><font size="3"><strong><br /><font size="4">[Reference]<br /></font></strong><br />Brookes AJ, The essence of SNPs, Gene. 1999 Jul 8;234(2):177-86.<br /></font><br /></p>