noun, plural: satellite DNAs
A satellite DNA is a portion of the DNA consisting of tandem repeats of non-coding nucleotide sequences that occur in the genome. Tandem repeats are copies of nucleotide sequences that lie adjacent to each other. It may be repetition(s) of one or more nucleotides. For example, CG CG CG CG CG is a tandem repeat wherein the sequence CG is repeated five times.
A satellite DNA are (chiefly) non-coding; it does not code for a particular protein. The term satellite came from the observation of a satellite peak in density gradient centrifugation, which was found to be large centromeric tandem repeats.1 It is present mainly in the centromere and heterochromatin. It was thought to be part of the junk DNA because of the noncoding sequences. However, it may be doing a role in the centromere function as well as in the formation of the heterochromatin.
The length of a satellite DNA ranges from 1 to several base pairs. For instance, in humans, an alpoid DNA is a satellite DNA found in all chromosomes and consists of 170 base pairs. Another is the beta-satellite DNA found in the centromeres of chromosomes 1, 9, 13, 14, 15, 21, 22, and Y chromosome. It consists of 68 base pairs.
1 Kit, S. (1961). "Equilibrium sedimentation in density gradients of DNA preparations from animal tissues". J. Mol. Biol. 3 (6): 711–716.