"We were struck by how variable the mutation rate appears to be along the genome," says Martincorena. "Our observations suggest these bacteria have evolved a clever mechanism to control the rate of evolution in crucial areas of the genome."
Using population genetics techniques, the researchers were able to disentangle the effects of mutation rate and natural selection on mutations, settling a long-standing debate in the field. Scientists have long thought that the chances of a mutation occurring were independent of its value to an organism. Once the mutation had occurred, it would undergo natural selection, spreading through the population or being eliminated depending on how beneficial or detrimental the genetic change proved to be.
"For many years in evolution there has been an assumption that mutations occur randomly, and that selection 'cleans them up'," explains Martincorena. "But what we see here suggests that genomes have developed mechanisms to avoid mutations in regions that are more valuable than others."
Observations from studies of cancer genomes suggest that similar mechanisms may be involved in the development of cancers, so Luscombe and colleagues would now like to investigate exactly how this risk-managing gene protection works at a molecular level, and what role it may play in tumour cells.
|Contact: Sonia Furtado Neves|
European Molecular Biology Laboratory