Tandem repeat

Tandem repeats are a family of DNA sequences involving the repetition of a particular series of nucleotides, where those repetitions are found directly adjacent to each other. Tandem repeats can be sub-classified as follows:

  • Minisatellites, where 10-60 nucleotides are repeated
  • Microsatellites (sometimes short tandem repeats), where fewer than 10 nucleotides are repeated
  • Dinucleotide repeats, when exactly two nucleotides are repeated
  • Trinucleotide repeats, when exactly three nucleotides are repeated (as in trinucleotide repeat disorders)
  • Variable number tandem repeats (VNTRs) where the number of repeats is either not known or not relevant (i.e. when referring to tandem repeats in a generalist manner)

Variable number tandem repeats (VNTRs) can be exceptionally useful in telling two individuals apart in genetic fingerprinting. Because DNA polymerase is more likely to make an error where a nucleotide sequence is repetitive, the length of VNTRs is, as the name implies, variable between individuals as a consequence of insertions or deletions. This gives each individual a 'tag' that can be distinguished from other 'tags' by determining the length of the VNTR in electrophoresis.