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Encyclopedia > Single nucleotide polymorphism
DNA strand 1 differs from DNA strand 2 at a single base-pair location (a C/T polymorphism).
DNA strand 1 differs from DNA strand 2 at a single base-pair location (a C/T polymorphism).

A single nucleotide polymorphism, or SNP (pronounced snip), is a DNA sequence variation occurring when a single nucleotide - A, T, C, or G - in the genome (or other shared sequence) differs between members of a species (or between paired chromosomes in an individual). For example, two sequenced DNA fragments from different individuals, AAGCCTA to AAGCTTA, contain a difference in a single nucleotide. In this case we say that there are two alleles : C and T. Almost all common SNPs have only two alleles. Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... In biology, polymorphism can be defined as the occurrence in the same habitat of two or more forms of a trait in such frequencies that the rarer cannot be maintained by recurrent mutation alone. ... part of a DNA sequence A DNA sequence (sometimes genetic sequence) is a succession of letters representing the primary structure of a real or hypothetical DNA molecule or strand, The possible letters are A, C, G, and T, representing the four nucleotide subunits of a DNA strand (adenine, cytosine, guanine... A nucleotide is a chemical compound that consists of a heterocyclic base, a sugar, and one or more phosphate groups. ... For the programming language Adenine, see Adenine (programming language). ... For the similarly-spelled vitamin compound, see Thiamine Thymine, also known as 5-methyluracil, is a pyrimidine nucleobase. ... Cytosine is one of the 5 main nucleobases used in storing and transporting genetic information within a cell in the nucleic acids DNA and RNA. It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an amine group at position 4 and a keto group at... Guanine is one of the five main nucleobases found in the nucleic acids DNA and RNA; the others being adenine, cytosine, thymine, and uracil. ... In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ... For the hard rock band, see Allele (band). ...


Within a population, SNPs can be assigned a minor allele frequency - the ratio of chromosomes in the population carrying the less common variant to those with the more common variant. It is important to note that there are variations between human populations, so a SNP allele that is common in one geographical or ethnic group may be much rarer in another. In the past, single nucleotide polymorphisms with a minor allele frequency of less than or equal to 1% (or 0.5%, etc.) were given the title "SNP," an unwieldy definition. With the advent of modern bioinformatics and a better understanding of evolution, this definition is no longer necessary. Given a Single Nucleotide Polymorphism (SNP), its minor allele frequency is the frequency of the SNPs less frequent allele in a given population. ... Map of the human X chromosome (from the NCBI website). ...


Single nucleotide polymorphisms may fall within coding sequences of genes, non-coding regions of genes, or in the intergenic regions between genes. SNPs within a coding sequence will not necessarily change the amino acid sequence of the protein that is produced, due to degeneracy of the genetic code. A SNP in which both forms lead to the same polypeptide sequence is termed synonymous (sometimes called a silent mutation) - if a different polypeptide sequence is produced they are non-synonymous. SNPs that are not in protein-coding regions may still have consequences for gene splicing, transcription factor binding, or the sequence of non-coding RNA. Diagram of the location of introns and exons within a gene. ... An Intergenic region is a stretch of DNA sequences located between clusters of genes that comprise a large percentage of the human genome but contain few or no genes. ... This article is about the class of chemicals. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... For a non-technical introduction to the topic, see Introduction to Genetics. ... Silent mutations or synonymous mutations are DNA mutations that, although they alter a particular codon, they do not alter the final amino acid, and hence do not affect the final protein. ... Genetic engineering, genetic modification (GM), and gene splicing (once in widespread use but now deprecated) are terms for the process of manipulating genes in an organism, usually outside of the organisms normal reproductive process. ... In molecular biology, a transcription factor is a protein that binds DNA at a specific promoter or enhancer region or site, where it regulates transcription. ... A non-coding RNA (ncRNA) is any RNA molecule that is not translated into a protein. ...


Variations in the DNA sequences of humans can affect how humans develop diseases and respond to pathogens, chemicals, drugs, vaccines, and other agents. However, their greatest importance in biomedical research is for comparing regions of the genome between cohorts (such as with matched cohorts with and without a disease). This article is about the medical term. ... A pathogen or infectious agent is a biological agent that causes disease or illness to its host. ... A chemical substance is any material substance used in or obtained by a process in chemistry: A chemical compound is a substance consisting of two or more chemical elements that are chemically combined in fixed proportions. ... This article does not cite any references or sources. ... A vaccine is an antigenic preparation used to establish immunity to a disease. ... A cohort was a sub-division of the Roman infantry, originally of a Roman legion, consisting of 480 men, itself divided in 6 centurias commanded each by a centurion. ...


The study of single nucleotide polymorphisms is also important in crop and livestock breeding programs (see genotyping). See SNP genotyping for details on the various methods used to identify SNPs. Genotyping refers to the process of determining the genotype of an individual with a biological assay. ... Genotyping provides a measurement of the genetic variation between members of a species. ...


See also

The Single Base Extension (SBE) is a biological reaction, which can follow after a PCR (Polymerase Chain Reaction). ... Variome is the whole set of variation found in populations of species that have gone through a relatively short evolution change. ... This article or section is in need of attention from an expert on the subject. ... Affymetrix Logo Affymetrix NASDAQ: AFFX was founded by Stephen P.A. Fodor, Ph. ... The goal of the International HapMap Project is to develop a haplotype map of the human genome, also referred to as the HapMap, which will describe the common patterns of human genetic variation. ... A tag SNP is a representative single nucleotide polymorphisms (SNPs) in a region of the genome with high linkage disequilibrium (the non-random association of alleles at two or more loci). ...

References

External links


  Results from FactBites:
 
Single nucleotide polymorphism - Wikipedia, the free encyclopedia (593 words)
A Single Nucleotide Polymorphism or SNP (pronounced snip) is a DNA sequence variation occurring when a single nucleotide - A, T, C, or G - in the genome (or other shared sequence) differs between members of a species (or between paired chromosomes in an individual).
SNPs within a coding sequence will not necessarily change the amino acid sequence of the protein that is produced, due to redundancy in the genetic code.
SNPs that are not in protein coding regions may still have consequences for gene splicing, transcription factor binding, or the sequence of non-coding RNA.
SNPs: Variations on a Theme (1601 words)
SNP variation occurs when a single nucleotide, such as an A, replaces one of the other three nucleotide letters—C, G, or T. An example of a SNP is the alteration of the DNA segment AAGGTTA to ATGGTTA, where the second "A" in the first snippet is replaced with a "T".
SNPs found within a coding sequence are of particular interest to researchers because they are more likely to alter the biological function of a protein.
Finding single nucleotide changes in the human genome seems like a daunting prospect, but over the last 20 years, biomedical researchers have developed a number of techniques that make it possible to do just that.
  More results at FactBites »

 
 

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