Satellite DNA

Satellite DNA consists of very large arrays of tandemly repeating, non-coding DNA. Satellite DNA is the main component of functional centromeres, and form the main structural constituent of heterochromatin.

The name "satellite DNA" refers to how repetitions of a short DNA sequence tend to produce a different frequency of the bases adenine, cytosine, guanine and thymine, and thus have a different density from bulk DNA - such that they form a second or 'satellite' band when genomic DNA is separated on a density gradient.

Satellite DNA, together with minisatellite and microsatellite DNA, constitute the tandem repeats.

Some types of satellite DNA in humans are:

A repeated pattern can be between 1 base pair long (a mononucleotide repeat) to several thousand base pairs long, and the total size of a satellite DNA block can be several megabases without interruption. Most satellite DNA is localized to the telomeric or the centromeric region of the chromosome. The nucleotide sequence of the repeats is fairly well conserved across species. However, variation in the length of the repeat is common. For example, minisatellite DNA is a short region (1-5kb) of 20-50 repeats. The difference in how many of the repeats is present in the region (length of the region) is the basis for DNA fingerprinting.

Microsatellites are thought to have originated by polymerase slippage during DNA replication. This comes from the observation that microsatellite alleles usually are length polymorphic; specifically, the length differences observed between microsatellite alleles are generally multiples of the repeat unit length.

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