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.^[1][2]

The name "satellite DNA" refers to how repetitions of a short DNA sequence tend to produce a different frequency of the nucleotides 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.^{[citation needed]}

Types of satellite DNA

Satellite DNA, together with minisatellite and microsatellite DNA, constitute the tandem repeats.^{[citation needed]}

Some types of satellite DNA in humans are:

Type	Size of repeat unit (bp)	Location
α (alphoid DNA)	171	All chromosomes
β	68	Centromeres of chromosomes 1, 9, 13, 14, 15, 21, 22 and Y
Satellite 1	25-48	Centromeres and other regions in heterochromatin of most chromosomes
Satellite 2	5	Most chromosomes
Satellite 3	5	Most chromosomes

Length

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 a 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.^{[citation needed]}

Origin

Satellite DNA, at least the microsatellite variety, is thought to have originated by slippage of a replicated chromosome against its template.^{[citation needed]}

Pathology

Microsatellites are often found in transcription units. Often the base pair repetition will disrupt proper protein synthesis, leading to diseases such as myotonic dystrophy.^{[citation needed]}

See also

• Polymerase chain reaction
• Gene expression

References

1. ^ Knight, Julian C. (2009). Human Genetic Diversity: Functional Consequences for Health and Disease. Oxford University Press. p. 167. ISBN 9780199227693. http://books.google.com/books?id=NSLeurRJWsIC&pg=PA167. 
2. ^ "satellite DNA" at Dorland's Medical Dictionary

Further reading

• Beridze, Thengiz (1986). Satellite DNA. Springer-Verlag. ISBN 978-0387158761. 
• Hoy, Marjorie A. (2003). Insect molecular genetics: an introduction to principles and applications. Academic Press. p. 53. ISBN 9780123570314. http://books.google.com/books?id=MPkwi-i33zYC&pg=PA53. 

External links

• MeSH Satellite+DNA