satellite DNA Any DNA which differs enough in its base composition to form a separate fraction from the majority of genomic DNA on centrifugation. This bias in base composition is often due to highly repetitious DNA. Satellite DNA may consist of dispersed repeats (e.g. long interdispersed elements and short interdispersed elements) or may be arranged in a tandem array. In a tandem array it may have very short repeating units, 2–10 base pairs in the case of microsatellite DNA, or slightly longer ones, 10–100 base pairs in the case of minisatellite DNA. The number of repeating units within a single satellite tandem array changes rapidly in evolutionary terms, due to the processes of replication slippage and unequal crossing over. Consequently, the length of an array can be used as a highly informative character in phylogenetic analysis at the intraspecific level. By using many such arrays a highly specific set of character states can be established, by which an individual organism may be identified; this is a DNA fingerprint.

satellite DNA A fraction of DNA that separates from the bulk of DNA when native DNA is separated according to density in a solution of caesium chloride following ultracentrifugation. The caesium chloride forms a density gradient and the DNA settles out where its density equals that of the solution. DNA from chloroplasts, mitochondria, ribosomes, and centromeres can form satellites. The term is commonly taken to include repetitive DNA, in which base sequences are repeated many times in the genome of a cell (e.g. heterochromatin may contain highly repetitive DNA with the base sequences repeated more than 1000 times).

satellite DNA The proportion of the DNA of a eukaryotic cell that consists of very large numbers (approximately 10⁶) of copies of a short nucleotide sequence. It occurs mainly around the centromeres and telomeres of the chromosomes. The highly repetitive nature of this DNA fraction gives it a distinctive base composition, and consequently when samples of DNA are centrifuged it forms so-called ‘satellite bands’ quite separate from the band representing the bulk of the cell's DNA. See repetitive DNA. Compare microsatellite DNA; variable number tandem repeats.