Satellite DNA consists of very large arrays of tandemly

Tandemly arrayed genes

Tandemly arrayed genes are a gene cluster created by tandem duplications. They serve to encode large numbers of genes at a time. An example are tandem clusters of rRNA encoding genes. These genes are translated faster than they would be if only a single copy of the gene was available.-See also:*...

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

Heterochromatin

Heterochromatin is a tightly packed form of DNA, which comes in different varieties. These varieties lie on a continuum between the two extremes of constitutive and facultative heterochromatin...

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The name "satellite DNA" refers to how repetitions of a short DNA

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 sequence tend to produce a different frequency of the nucleotides adenine

Adenine

Adenine is a nucleobase with a variety of roles in biochemistry including cellular respiration, in the form of both the energy-rich adenosine triphosphate and the cofactors nicotinamide adenine dinucleotide and flavin adenine dinucleotide , and protein synthesis, as a chemical component of DNA...

, cytosine

Cytosine

Cytosine is one of the four main bases found in DNA and RNA, along with adenine, guanine, and thymine . It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached . The nucleoside of cytosine is cytidine...

, guanine

Guanine

Guanine is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine . In DNA, guanine is paired with cytosine. With the formula C5H5N5O, guanine is a derivative of purine, consisting of a fused pyrimidine-imidazole ring system with...

 and thymine

Thymine

Thymine is one of the four nucleobases in the nucleic acid of DNA that are represented by the letters G–C–A–T. The others are adenine, guanine, and cytosine. Thymine is also known as 5-methyluracil, a pyrimidine nucleobase. As the name suggests, thymine may be derived by methylation of uracil at...

, 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

Density Gradient

Density gradient is a spatial variation in density over an area. The term is used in the natural sciences to describe varying density of matter, but can apply to any quantity whose density can be measured...

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Types of satellite DNA

Satellite DNA, together with minisatellite

Minisatellite

A minisatellite is a section of DNA that consists of a short series of bases 10-60 bp. These occur at more than 1,000 locations in the human genome...

 and microsatellite DNA, constitute the tandem repeats.

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

Minisatellite

A minisatellite is a section of DNA that consists of a short series of bases 10-60 bp. These occur at more than 1,000 locations in the human genome...

 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.

Origin

Satellite DNA, at least the microsatellite variety, is thought to have originated by slippage of a replicated chromosome against its template.

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

Myotonic dystrophy

Myotonic dystrophy is a chronic, slowly progressing, highly variable inherited multisystemic disease. It is characterized by wasting of the muscles , cataracts, heart conduction defects, endocrine changes, and myotonia. Myotonic dystrophy can occur in patients of any age...

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