Single nucleotide polymorphism

From Freepedia

A Single Nucleotide Polymorphism or SNP (pronounced snip) is a DNA sequence variation, occurring when a single nucleotide: adenine (A), thymine (T), cytosine (C) or guanine (G) - in the genome is altered. For example, a SNP might change the nucleotide sequence AAGCCTA to AAGCTTA. A variation must occur in at least 1% of the population to be considered a SNP.

SNPs make up 90% of all human genetic variations, and occur every 100 to 300 bases along the human genome. Two of every three SNPs substitute cytosine (C) with thymine (T). Variations in the DNA sequences of humans can affect how humans respond to diseases, bacteria, viruses, chemicals, drugs, etc.

SNPs are of great value to biomedical research and in developing pharmacy products. Because SNPs do not change much from generation to generation, following them during population studies is straightforward. They are also used in some forms of genealogical DNA testing.

SNPs are generally considered to be a form of point mutation that has been evolutionarily successful enough to recur in a significant proportion of a species' population.

Detection

A convenient method for detecting SNPs is restriction fragment length polymorphism (SNP-RFLP). If one allele contains a recognition site for a restriction enzyme while the other does not, digestion of the two alleles will give rise to fragments of different length. If no such discriminatory restriction sites exist, they can often be introduced by polymerase chain reaction (PCR).

References

• Human Genome Project Information — SNP Fact Sheet

External links

• The SNP Consortium LTD — SNP search
• NCBI dbSNP database — "a central repository for both single base nucleotide subsitutions and short deletion and insertion polymorphisms"
• International HapMap Project — "a public resource that will help researchers find genes associated with human disease and response to pharmaceuticals"
• Glovar Variation Browser — variation information in a genomic context
• WatCut — an online tool for the design of SNP-RFLP assays