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.
An example would be: ATTCG ATTCG ATTCG in which the sequence ATTCG is repeated three times.
Terminology[change | change source]
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[change | change source]
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.
Reference[change | change source]
- 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.