Single Nucleotide Polymorphism

With single-nucleotide polymorphisms (SNP, English Single Nucleotide Polymorphism; pronounced. Snip ) variations of individual base pairs are referred to in a DNA strand. The definition that SNPs must occur in at least 1 % of the relevant population, is after the introduction of the latest molecular genetic methods in practice no longer relevant.

SNPs represent about 90 % of all genetic variants in the human genome represents; they do not occur uniformly distributed on, but only irregularly strong in certain regions. Two thirds of all SNPs consist of the replacement of cytosine by thymine, cytosine as in the vertebrate genome is frequently methylated. By spontaneously occurring deamination of 5- methylcytosine is thymine. Depending on the base exchange the information of the codon can be altered. Encodes the triplet continue for the same amino acid is called a synonymous SNPs. In a non-synonymous SNP was one amino acid change. If a non- synonymous SNP in a coding region, CSNP ( codingSNP ), a modified base have an effect on protein function and draw physiological defects after themselves. An equally large group of SNPs to a disturb gene regulation, rSNP ( regulatorySNP ). These are frequently regulatory regions in and influence the transcription, and hence the protein concentration. Second, the RNA processing of srSNP ( structural RNASNP ) may be disturbed. For example, can cause a base change at a splice to an mRNA, which codes for a nonfunctional protein.

SNPs are generally referred to as " successful " point mutations, that is, as genetic changes that have prevailed to some extent in the gene pool of a population. Some SNPs correlate such as specific reactions of the organism to treat certain infections or contact with specific substances.

Their scientific importance lies in the frequent occurrence and the high variability, also they are very quick and easy to determine. That is why they are used for example in the search for quantitative trait loci, ie chromosome segments with influence on the expression of a quantitative trait, for the identification of individuals and in relationship diagnoses, but also in research for drug compatibility and the like.