Genes with the ability to jump around the genome play a bigger role in maintaining human genetic diversity than previously thought, with major implications for the study of evolution as well as contributing to the disruption of genes causing genetic disease.

 Jumping genes - or transposons - are stretches of DNA that can insert themselves at different locations in the genome of the same cell.

 US researchers looked at the germ cells (i.e. the egg and sperm cells that carry the heritable genetic material) of 25 people, 15 of whom were unrelated. Using high throughput sequencing methods they mapped 1139 insertion sites, from across the genome, of a common class of jumping genes called retrotransposons. They then calculated that any two given genomes will differ at around 285 of these sites, a much higher number than expected.

 Professor Haig Kazazian, from the University of Pennsylvania, who conducted the research said: 'The significance of this work is that there is much more diversity in our genome due to insertions by this family of transposons than previously thought. This movement of genetic material provides the raw material of genetic evolution, and it doesn't take into account the insertions that we believe occur outside of the sperm and egg cells studied in this project'.

 Genetic diversity within a population is crucial, with small genetic changes helping organisms to adapt to new environments and reducing vulnerability to disease. The potential of retrotransposons to contribute to this diversity stems from two important characteristics. When retrotransposons jump from one genomic site to another they, firstly, leave a copy of themselves behind and, secondly, can take sections of surrounding sequences with them to the new insertion site. Continual jumping will therefore eventually result in an expansion of the genome and a re-ordering of the genetic material; it may even lead to the creation of new genes.

 While insertions of the transposon into the genome are often harmless, there are certain sites that, when disrupted, can have major implications for disease. For example, insertion into genes responsible for cell function can lead to the dysregulation of many cellular processes, including those that protect against the development of cancer. Duchenne muscular dystrophy and haemophilia are two examples of genetic diseases where this mechanism has been observed. Perhaps exploring the behaviour of retrotransposons may aid the quest to improving the understanding of such diseases.

The study is published online in Genome Research.