Satellite DNA

Satellite DNA or tandemly repeated DNA are DNA sequences highly repetead present on heterochromatin and also found at centromeres, being made up by short and simple sequences that form big sequence blocks. It is a common feature of eukaryotic genomes but is found less frequently in prokaryotes. 

They are known as satellites because DNA fragments containing tandemly repeated sequences form different bands when genomic DNA is fractionated by density gradient centrifugation.

There are two types of satellite DNA, known as microsatellies and minisatellites, where microsatellites clusters are shorter than minisatellites. For example, Huntington’s disease it’s due to the (CAG)n sequence extension caused by microsatellite CAG in the gene enconding for the huntingtin protein.