Genetic changes that appear in an organism DNA It may not be completely random, new research suggests. This will overturn one of the main assumptions of The theory of evolution.
Researchers who study genetic mutations In a common roadside grass, cress (Arabidopsis thaliana), that a plant can protect the “essential” genes in its DNA from changes, while leaving other sections of its genome to make further alterations.
“I was completely surprised by the non-random mutations that we discovered,” lead author Gray Munro, a botanist at the University of California, Davis, told Live Science. Since high school biology, I’ve been told that mutations are random.”
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Random mutations are an important part of the theory of evolution by natural selection, in which mutations lead to adaptations that are passed on to offspring and alter their chances of survival. Scientists assumed that these mutations were random and that the first step in evolution by natural selection was, therefore, also random. The new study suggests that this may not be entirely true.
“The idea of random mutations has been around for over a hundred years in biology and it’s something you hear a lot as a student and it’s easy to take for granted,” Munro said. “Even as a practicing geneticist and evolutionary biologist, I’ve never seriously questioned the idea.”
The new discovery does not refute or distort the theory of evolution, and the researchers said that randomness still plays a large role in mutations. But the study shows that these genetic modifications are more complex than scientists previously thought.
There are plenty of opportunities for genetic mutations and even errors to occur during an organism’s lifetime.
“DNA is a fragile molecule; on average, DNA is damaged in a single cell between 1,000 and a million times each day,” Munro said. “DNA also has to be transcribed every time a cell divides, which can lead to errors in transcription.”
Fortunately for humans and all other living things, our cells can fend off much of this damage. “Our cells are constantly working to correct DNA, and they have developed complex molecular machines, DNA repair proteins, to look for errors and make repairs,” Munro said.
However, DNA repair proteins are not a foolproof solution and cannot fix all errors. “If the damage or transcription errors are not repaired, it causes a mutation and a change in the DNA sequence,” Munro said.
There are two main types of mutations: somatic mutations, which cannot be passed on to offspring, and germline mutations, in which the offspring can inherit a DNA error from a gene mutated in one of the parents. Germline mutations are what fuel evolution by natural selection and become more or less common in a population depending on how they affect the viability of the vector.
Not all mutations have the ability to change an organism’s chances of survival. Mutations cause major changes in an organism only when they occur in genes – parts of DNA that code for a specific protein. Monroe said most of the human genome is made of non-genetic DNA.
In the new study, the researchers decided to test the randomness of the mutations by checking whether the mutations occur equally between the genetic and non-genetic regions of DNA in the cress genomes.
Cressa thele is a “cool model organism” for mutagenicity because its genome contains only about 120 million base pairs (for comparison, the human genome contains 3 billion base pairs), which makes it easy to sequence plant DNA. It also has a very short life span, Munro said, which means that mutations can quickly accumulate across multiple generations.
Over a three-year period, researchers have grown hundreds of plants in laboratory conditions for several generations. In total, the researchers sequenced 1,700 genomes and found more than one million mutations. But when they analyzed these mutations, they found that the parts of the genomes that contained the genes had much lower mutation rates than the non-genetic regions.
“We think it’s possible that other organisms may also have nonrandom gene mutations,” Munro said. “We have already followed up on our study by investigating this question in other species and found results indicating that the non-random mutation is not unique. Arabidopsis. “
However, the researchers suspect that the level of non-randomness between the different species may not be the same.
Protecting essential genes
The non-random pattern in the mutations between the genetic and non-genetic regions of DNA suggests that there is a defense mechanism to prevent potentially catastrophic mutations.
“In genes coding for proteins essential for survival and reproduction, mutations are more likely to have adverse effects, potentially causing disease and even death,” Munro said. “Our results show that genes, and core genes in particular, experience a lower mutation rate than non-genetic regions of Arabidopsis. The result is that the offspring have a lower chance of inheriting a harmful mutation.”
The researchers found that to protect themselves, essential genes send special signals to DNA repair proteins. This signal is not made by the DNA itself but by histones, the DNA of specialized proteins wraps around to form chromosomes.
“Based on the result of our study, we found that gene regions, especially for the most biologically important genes, wrap around histones with certain chemical markers,” Munro said. “We believe these chemical markers act as molecular cues to promote DNA repair in these regions.”
The idea of histones with unique chemical markers isn’t new, Munro said. He added that previous studies of mutations in cancer patients have also found that these chemical markers can influence whether DNA repair proteins repair mutations properly.
However, this is the first time that the effect of these chemical markers has been shown on the patterns of mutations at the genome level and, as a consequence, on evolution by natural selection.
The researchers hope that their findings can eventually be used to make improvements in human medicine.
Mutations affect human health in many ways, being the cause of cancerand genetic disease and aging.” He added that the ability to protect specific regions of the genome from mutations could help prevent or treat these problems.
However, more research into the animal genome is needed before researchers can tell whether the same non-random mutations occur in humans. “Our discoveries were made in plants and do not lead to new treatments, but they have changed our basic understanding of the mutation and inspire many new research directions,” Munro said.
Researchers also believe that chemical signals from essential genes can be used for reinforcement Gene editing techniques It could help us produce crops that are more nutritious and resilient to climate change, Munro said.
The study was published online January 12 in the journal temper nature.
Originally published on Live Science.