Confirming a long-standing hypothesis, scientists from the Netherlands' Leiden University have shown that the genetic information in the DNA not only determines who we are, but also the DNA mechanics.

Since the mid-1980s it has been hypothesised that there is a second layer of information on top of the genetic code: DNA's mechanical properties.

Each of our cells contains two meters of DNA molecules, so these molecules need to be wrapped up tightly to fit inside a single cell.

The way in which DNA is folded, determines how the letters are read out, and therefore which proteins are actually made.

In each organ, only relevant parts of the genetic information are read, based on how the DNA is folded.

The theory goes that mechanical cues within the DNA structures determine how DNA prefers to fold.

In a study published in the journal PLoS One, Leiden physicist Helmut Schiessel and his research group provided strong evidence that this second layer of information indeed exists.

With their computer code they simulated the folding of DNA strands with randomly assigned mechanical cues.

It turns out that these cues indeed determine how the DNA molecule is folded into so-called nucleosomes.

Schiessel found correlations between the mechanics and the actual folding structure in the genome of two organisms ? baker's yeast and fission yeast.

With this finding we know that evolutionary changes in DNA ? mutations ? can have two very different effects.

The letter sequence encoding for a specific protein can change or the mechanics of the DNA structure can change, resulting in a different packaging and accessibility of the DNA and therefore a different frequency of production of that protein.