Evolution study suggests DNA mutations are less random than we thought

The DNA mutations that drive evolution are generally thought to be somewhat random, but a new study suggests there is some order to this mess. By comparing the genomes of hundreds of plants grown in the laboratory, a team of scientists found that mutations are much less likely to occur in genes necessary for survival.

Chance plays a big role in evolution. Conventional thinking goes that DNA mutations will arise randomly in an organism’s genome, and if these new traits occur to help an organism survive and reproduce, those mutations will be passed on to the next generation. Over a sufficiently long period, a trait can become a feature of a population or species.

But is there a pattern for where in the genome DNA mutations occur? To investigate, researchers from the University of California at Davis and the Max Planck Institute grew hundreds of cress plants in the lab, then sequenced their genomes and compared where the DNA mutations occurred — and a non-random pattern appeared to emerge.

“We’ve always thought that the mutation was essentially random across the genome,” says Gray Munro, the study’s lead author. “It turns out that the mutation is not very random and it is not random in a way that benefits the plant. It is a completely new way of thinking about mutations.”

By growing the plants under controlled laboratory conditions, the team sought to remove the nonrandom effect of natural selection, ensuring that plants that do not normally live in the real world would not be decimated by any negative mutations.

Within the hundreds of plant genomes, the team has identified more than a million mutations, which appear to be concentrated in specific parts of the genome. This has left patches with consistently low mutation rates, as low as a third of those in other regions. When the scientists examined the genes in those spots, they found an abundance of essential genes, including those involved in cell growth and gene expression.

“These are the really important regions of the genome,” Munro says. “The areas that are most biologically important are the areas protected from mutations.”

Interestingly, these regions also appear to have stronger DNA damage repair mechanisms, suggesting a kind of enhancement method to ensure that these crucial sequences continue to function.

“The plant has developed a way to protect its most important places from mutations,” says Detlev Weigl, senior author of the study. “This is exciting because we can even use these discoveries to think about how to protect human genes from mutations.”

The new research adds to a growing body of work that deepens our understanding of the role of DNA mutations in evolution. A 2014 study found that mutations occur more frequently near repeating sequences, while another study from 2019 identified mutation hotspots at recombination sites, where chromosomes from each parent pair together.

Researchers in the new study say this work could eventually lead to improvements in engineering better crops, and even controlling human diseases caused by DNA mutations, such as some cancers. But there is no doubt that any applications in these areas remain elusive.

Publish the research in the journal temper nature.

Source: University of California at Davis

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