Introduction:
Satellite DNA (satDNA) also known as tandemly repeated DNA (TR-DNA), is the highly repetitive DNA consisting clusters of short repeated sequences i.e., same sequence of nucleotides is repeated many times in tandem within the genome.
Generally, it possesses a variable AT-rich repeat which are predominately located at heterochromatic regions, which are found mostly in centromeric, pericentromeric and sub-telomeric regions in the chromosomes but also at intercalary positions. The sequences are also particularly common in mammalian Y chromosomes.
Although, Satellite DNA has been known to be ‘non-coding’ (i.e., it does not code for any amino acid), however, some recent study has reported that some of the satellite DNA does undergo transcription and code protein eventually.
Fig: Satellite DNA (satDNA)/Tandemly repeated DNA (TR-DNA)
Types:
It is divided into several categories according to the size of the individual repeats.
Microsatellites
Itconsists of very small repeat sequences 1 to 9 bp which is 10 to 100 times, and which is located in various places in the euchromatic portion of the genome.
Short tandem repeats (STRs)
This have repeat lengths of 3 to 5 bp, and are repeated 10 to 100 times in various genomic locations.
Minisatellites
It varies in repeat size from 10 to 100 bp (usually about 15 bp). They are usually found in clusters of 10 to 100 repeats that is located in euchromatic sub- telomeric regions or dispersed in other areas of the genome.
Macrosatellites
It varies in repeat size ranging from more than 100 bp (usually about 15 bp). They are dispersed in different areas of the genome.
Features:
- In one species, different families of satDNA may be present such as 15 families in Pisum sativum, 62 families in Locusta migratoria, or 9 satDNA families within the human genome.
- However, each species possesses usually one or a few predominant satDNA families. For example, the centromeric α satDNA which is the most abundant satDNA family the human genome represents more than half of the total content of satDNA.
- More than 10 percent of our genome is made up of satDNA that do not code for any proteins which is also referred to as “genomic junk.”
- The DNA of every human on the earth is 99.9% the same. However, about 0.1% of DNA is unique in every individual.
- Human genome possesses numerous small non-coding that do not code for proteins but make-up 95% of our genetic DNA and therefore known as “Junk DNA”.
Applications:
The short repeat sequences of DNA stretch in satellite DNA vary from one individual to other. Thus, this variations in the sequence and length of satDNA are unique to each induvial human and moreover, this uniqueness and be applied in various research, comparison, identification, and diagnosis approach.
- Genetic Mapping: Construction of physical map and genetic linkage.
- Population Genetics: To explore the genetic diversity, population and evolutionary data.
- Conservation Biology: To access genetic diversity in endangered species.
- Comparative Genomics: To study the chromosomal arrangements and genome evolution.
- Forensic Sciences: Human proof of identity and paternity testing.
- Cancer Research: Potential biomarkers in cancer diagnosis and its prognosis.
- Species Identification: Species identification and biodiversity assessment.