noun, plural: tandem repeats
(molecular biology) A type of repeated sequence in which the copies are repeated one after another along a chromosome
The repeated sequences occur as multiple copies of nucleic acids in the genome. These repeats may involve the DNA or the RNA. There are three major types of repeated sequences: (1) terminal repeats, (2) tandem repeats, and (3) interspersed repeats.
Tandem repeats are repeated nucleotide sequences in which the copies lie adjacent to each other. It may be repetition(s) of one or more nucleotides. For example, CG CG CG CG CG is a tandem repeat wherein the sequence CG is repeated five times.
Tandem repeats include satellite DNAs, microsatellites, and minisatellites. Satellite DNA is a tandem repeat wherein the DNA copies are chiefly non-coding. It is present mainly in the centromere and heterochromatin. A microsatellite is a small tandem repeat ranging in length from 1-6 or more base pairs, repeated typically five to fifty times. A minisatellite is also a small tandem repeat but with relatively longer base pairs, i.e. from 10 to 60 base pairs, repeated typically five to fifty times.
Examples of tandem repeats are the 40S rRNA genes in somatic cells of toads, of which there are about 500 copies.