Repetitive DNA is distributed into 1000 to 40,000 families. All the repetitive DNA present in the genome could be broadly categorized into two: tandem repeats and dispersed repeats. Centromeres, telomeres and chromosome knobs fall under tandem repetitive DNA; and transposons and retrotransposons under dispersed repeats. In tandemly repetitive DNA, the repeat sequences are present contiguously one after the other, where as the repeat sequences of dispersed repeats are scattered throughout the genome. The repetitive DNA contributes to the character and function of specialized structures and chromosomes. It also plays an important role in genome organization.
The noncoding tandem repetitive DNA is also known as satellite DNA, as it forms a separate zone from the rest of the DNA during the CsCl density gradient centrifugation. The satellite DNA of most animals and yeast tend to be AT-rich; however, in plants, it is generally GC-rich. The satellite DNA is primarily associated with either the centromere or telomere. It is usually heterochromatic and condensed.