Categories of repetitive DNA in the human genome

    More than half of the human genome consists of non-protein-coding, repetitive DNA elements. These occur in several classes with specific characteristics. The most important of these are highly-repetitive DNAs that  are detected as satellite DNA in ultracentrifuge experiments.These may be arranged either as tandem repeats where specific short DNA sequences are repeated in end-to-end arrays from a few to many tens of times, or as interspersed repeats in which a particular sequence occurs at hundreds or thousands of separate locations. Tandem microsatellites comprise two-letter motifs, minisatellites typically comprise four- or six-letters motifs; both occur in variable numbers per locus. Interspersed repeats may be short (SINEs) or long (LINEs), for which the characteristic human families are Alu (200~300 bp) and L1 (6,400 bp), respectively. Other important SINEs include the Alphoid (170 bp) family that constitutes centromeric heterochromatin.

Figure © 2000 by Klug & Cummings; all text material © 2014 by Steven M. Carr