The findings of a new study have dramatically challenged the established theory of evolution. For years, we have believed that genetic mutations occur randomly – but according to new research, they may be much less random than originally thought.
The idea that mutations occur randomly across the genome is widely accepted as true. In fact, the current evolutionary theory relies on this randomness. It states that natural selection acts on random genetic variation, resulting in certain characteristics becoming more or less common in a population.
However, recent research has revealed that many factors, such as nucleotide composition, can influence the likelihood that mutations will occur at specific locations. Previous studies have also found evidence that DNA repair is targeted to specific regions.
The team behind the new study investigated these ideas further to find out whether genetic mutations are truly random.
Non-random mutation rates
The scientists collected DNA from Arabidopsis thaliana plants, also known as thale cress. Next, they compiled large sets of de novo mutations in thale cress. This was done to make sure that any mutations found had not yet undergone natural selection. Over the course of three years, the team sequenced and analysed the DNA samples. This uncovered more than one million mutations.
The team tested whether there were any patterns in the location of mutations across the genome. Interestingly, they found that mutation frequency was 58% lower in transcriptional regions of genes than in intergenic regions. Further analysis confirmed that a lower mutation rate, rather than selection, was the cause of the observed lower frequency of mutation.
Fewer mutations in essential genes
Next, the researchers investigated whether there were links between mutation rates and gene functions. It was found that patches of the genome with low mutation rates were enriched for essential genes with conserved biological functions. Contrastingly, genes which had environmentally conditional functions had very high mutation rates. These results suggested to the researchers that these essential areas of the genome were being protected from mutation due to their importance.
“These are the really important regions of the genome,” said lead author Grey Monroe. “The areas that are the most biologically important are the ones being protected from mutation.”
The role of the epigenome
When the researchers looked at the thale cress genome in more detail, they found that essential genes had a greater number of epigenomic features associated with low mutation rate. Such features are able to recruit DNA repair factors, thereby reducing the frequency of mutations.
This finding reveals a potential method for predicting whether a gene is likely to mutate or not. It also suggests that the plant has evolved to protect its essential genes from mutation. Therefore, the mutations occurring in the plant are not random at all.
Looking to the future
These findings have the potential to completely change how we think about mutation and evolution.
“We always thought of mutation as basically random across the genome,” said Monroe. “It turns out that mutation is very non-random and it’s non-random in a way that benefits the plant. It’s a totally new way of thinking about mutation.”
The implications of these results are wide-reaching. Knowing which regions of the genome have higher mutation rates could aid the development of more robust crops. Importantly, such information could also be used to better predict and treat human diseases that are caused by mutation, such as cancer.
“The plant has evolved a way to protect its most important places from mutation,” said Weigel. “This is exciting because we could even use these discoveries to think about how to protect human genes from mutation.”
Picture credit: Canva