SNP -- SINGLE NUCLEOTIDE POLYMORPHISM
[LAST REVISED 12 February 2001]
Single nucleotide polymorphisms (SNPs) are DNA sequence variations that occur when a single nucleotide (A,T,C,or G) in the genome sequence is changed. Most SNPs, actually about two of every three SNPs, involve the replacement of cytosine (C) with thymine (T). SNPs occur every 100 to 300 bases along the human genome. SNPs are stable from an evolutionarily standpoint --not changing much from generation to generation --making them easier to follow in population studies.
Several groups are working to find SNPs and ultimately create SNP maps of the human genome. Among these groups are the U.S. Human Genome Project and a large group of pharmaceutical companies called the SNP Consortium. The likelihood of duplication among the groups is small because of the estimated 3 million SNPs.
In 1998, as part of their latest five-year plan, the DOE and NIH Human Genome Programs established goals to identify and map SNPs. These goals are as follows:
--Develop technologies for rapid, large-scale identification and scoring of single-nucleotide polymorphisms and other DNA sequence variants.
--Identify common variants in the coding regions of most identified genes.
--Create a SNP map of at least 100,000 markers.
--Develop the intellectual foundations for studies of sequence variation.
--Create public resources of DNA samples and cell lines.
In the spring of 1999, some pharmaceutical companies and the U.K. Wellcome Trust philanthropy established a consortium headed by Arthur L. Holden to find and map 300,000 common SNPs. The goal is to generate a publicly available map using SNPs as markers evenly distributed throughout the human genome.
SNP data will be made available through a consortium Web site SNP Consortium at quarterly intervals during the project's first year and at monthly intervals during the second year. SNPs also will be deposited in the public dbSNP database dbSNP. Expectations are to have 150,000 SNPs mapped by mid-2001. For more on human polymorphisms, see HGBASE (Human Genic Bi-Allelic SEquences) --a human gene-based polymorphism database HGBASE
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