According to some researchers, it is the weakness in DNA structure that makes certain cells more likely to become cancerous.

The researchers studied a gene linked to a form of non-Hodgkin's Lymphoma.

The researchers are from the University of Southern California, USA.

Part of the gene was not arranged in the double helix structure, they noticed. This is a weakness in the gene. They were examining lymphocytes - immune system cells.

There is a gene in these cells which controls the self-destruction of the cells when they come to the end of their natural life term (suicide trigger). The gene is called Bcl-2.

If Bcl-2 is too active it can trigger the development of a non-Hodgkin's Lymphoma called follicular lymphoma.

The genes activity is disrupted when the chromosome (where the gene sits) number 18 breaks. It trades material with chromosome number 14. Scientists already knew this before their study. This area is called the 'weak point'.

The scientists examined this 'fragile site' (the weak point where gene break is most likely).

What they found was that the DNA was not arranged in the classic double helix formation in this fragile site or weak point.

Dr Michael Lieber, team leader said 'Of all the chromosomal fragile sites in cancer, this is the first one where we've actually understood why it's fragile. And it is because of this molecular quirk in the Watson-Crick helix. It is important to know how and why cancer begins. And this is an important step to understanding that - to understanding why the break is happening and why the chromosomes are swapping arms.'

He also said that there is more they need to know about the exact structure of the DNA at this fragile site. He admitted that their knowledge of the exact structure of the DNA is quite limited.