Index >> Deoxyribose Nucleic Acid - DNA >> Repetitive DNA (Satellite DNA)

Most vertebrate DNAs on the other hand do not reassociate easily; firstly because the degraded molecules form heterogenous populations, and secondly because of their much larger molecular weights (upto X 1,000) as compared to bacterial DNAs.

However, Britten and his cowor­kers (1966, 1968) have demonstrated that many vertebrate DNAs reasso­ciate, especially if broken into small pieces. This observation gave rise to the hypothesis that certain short sequences of bases are repeated hundreds of times in DNA. Such DNA has been called repetitive DNA or satellite DNA.

Repetitive DNA consists of short identical genes which are repeated in tandem several hundred or thousand times. Such DNA is found in the region of the chromosome adjacent to the centromere.

Each satellite DNA consists of a repeating sequence of 7 nucleotide pairs.

All eukaryotes, except perhaps yeast, contain repetitive DNA. In Drosophila about 25% of the DNA is of the repetitive type. In humans 30% of the DNA contains sequences which are repeated at least 20 times.

In the mouse 10% of the DNA is highly repetitive, and is half reassociated in a few seconds. About 20% is moderately repetitive and reassociates at an intermediate rate. 70% is single copy DNA which renatures very slowly.