Tandem repeat

Tandem repeats occur in DNA when a pattern of nucleotides is repeated. The repeats sit next to each other, in tandem. These are multiple copies of the same base-pair sequence lying end-to-end.Burt A. & Trivers R. 2006. Genes in conflict: the biology of selfish genetic elements. Harvard University Press. "Tandem Repeats" p364/6 & p582."Copies of base-pair sequences may be repeated one after another along a chromosome: for example the 40S rRNA genes in somatic cells of toads, of which there are about 500 copies". Adapted from Biology-Online.org  Tandem Repeat at the US National Library of Medicine Medical Subject Headings (MeSH) Alberts, Bruce et al 2002. Molecular biology of the cell. Garland, G31. 

An example would be:   ATTCG ATTCG ATTCG   in which the sequence ATTCG is repeated three times.

 Terminology 
If between 10 and 60 nucleotides are repeated, it is called a minisatellite. Those with fewer are known as microsatellites or 'short tandem repeats'.

When exactly two nucleotides are repeated, it is called a dinucleotide repeat (for example: ACACACAC…).

When three nucleotides are repeated, it is called a trinucleotide repeat (for example: CAGCAGCAGCAG…). Abnormalities in such regions can give rise to trinucleotide repeat disorders.

The repeat unit copy number may be variable. This is a variable number tandem repeat (VNTR). 

 Uses 
A tandem repeat pattern helps determine an individual's inherited traits. Tandem repeats can be very useful in determining parentage. Short tandem repeats are used for certain genealogical DNA tests.

In genetic fingerprinting and DNA profiling, DNA is examined from tandem repeats in the chromosomal DNA.  

 Reference 

Category:DNA