Variable number tandem repeat

From Wikipedia, the free encyclopedia

A variable number tandem repeats (VNTR) is a short nucleotide sequence ranging from 14 to 100 nucleotides long that is organized into clusters of tandem repeats, usually repeated in the range of between 4 and 40 times per occurrence. Clusters of such repeats are scattered on many chromosomes. Each variant is an allele and they are inherited codominantly.

Coupled with Polymerase chain reactions, VNTRs have been very effective in forensic crime investigations. When VNTRs are cut out, on either side of the sequence, by restriction enzymes and the results are visualized with a gel electrophoresis, a pattern of bands unique to each individual is produced. The number of times that a sequence is repeated varies between different individuals and between maternal and paternal loci of an individual. The likelihood of two individuals having the same band pattern is near impossible.

There are two principal families of VNTR: minisatellites and microsatelites. The former are sequences of 11-16 bp repeated till 1000 times. They are important because are highly repetitive and dispersed into the genome. in humans, they are present in 60 autosomic loci and they can be examined by digesting the DNA and hybriding with a monolocus probe or with another probe derived from a sequence that is common to each locus. The other members of VNTR family are the microsatellites or STR (short tandem repeats).They are represented by short sequences of 100-200 bp given by the repetition of 1-6 bp sequences. They can't be digested, so they are amplified by a multiplex PCR. Parental investigation with this kind of markers are non suitable between consanguineous, because electrophoresis profiles will be very similar. So it is possible to examine only one locus. In this way the system it's perfect: one allele derive from mother and the other one from father. Microsatellites have a lot of uses: they can be used in forensics, genetic variability and parentage studies.