Repetitive DNA

Repetitive DNA studies of many organisms has revealed that a large proportion of eukaryotic genomes consists of repetitive DNA.

For example in the kangaroo rat

• the sequence (AAG) is repeated 2.4 billion times,


• the sequence (TTAGGG) is repeated 2.2 billion times and


• the sequence (ACACAGCGGG) is repeated 1.2 billion times.

What it does is unclear. These are called junk DNA sequences.

Note that junk is stuff you don't throw away because it might be useful some day;
garbage is stuff you don't want so you throw it away.

These sequences might have some function we don't know about so they have been called junk DNA. The fact that such sequences seem to accumulate in genomes has lead to the notion that repetitive DNA is selfish DNA, since the sequence makes additional copies of itself within the genome decoupled from the reproduction rate of the host.