Satellite DNA contributes to the essential processes of formation of crucial chromosome structures, heterochromatin establishment, dosage compensation, reproductive isolation, genome stability and development.

Repeated sequences (also known as repetitive elements, repeating units or repeats) are patterns of nucleic acids (DNA or RNA) that occur in multiple copies throughout the genome. Repetitive DNA was first detected because of its rapid re-association kinetics.

Two main kinds of highly repetitive sequences are known in mammalian genomes: interspersed DNA, in which the repeated DNA sequences are dispersed throughout the genome; and satellite DNA which is characterised by long tandem arrays and consistent association with constitutive heterochromatin (Singer, 1982).

Tandem repeats are short lengths of DNA that are repeated multiple times within a gene, anywhere from a handful of times to more than a hundred. These sequences are also called VNTRs, or variable number tandem repeats, because different individuals within a population may have different numbers of repeats.

Repetitive DNA and Transposons. Repetitive DNA is composed of tandem, repeated sequences of from two to several thousand base pairs and is estimated to constitute about 30% of the genome. Many of these sequences are localized in centromeres and telomeres, but they are also dispersed throughout the genome.

Microsatellite refers to a set of short repeated DNA sequences at a particular locus on a chromosome, which varies in number in different individuals and so can be used for genetic fingerprinting while minisatellite refers to a form of polymorphic DNA, comprising a variable number of tandem repeats, with repeat units …

The number of repeats can be gauged by dividing the entire molecular weight of a given VNTR by the molecular weight of the repeated sequence. VNTRs are similar to Short Tandem Repeats (For more on STRs, see page 3), the difference being that in a VNTR, the repeated sequence is longer — about 10-100 base pairs long.

VNTRs are an important source of RFLP genetic markers used in linkage analysis (mapping) of genomes. They have become essential in forensic crime investigations. The technique may use PCR, size determined by gel electrophoresis, and Southern blotting to produce a pattern of bands unique to each individual.

DNA fingerprinting is a laboratory technique used to establish a link between biological evidence and a suspect in a criminal investigation. Conversely, if the two DNA profiles do not match, then the evidence cannot have come from the suspect. DNA fingerprinting is also used to establish paternity.