![]() "We think these chemical marks are acting as molecular signals to promote DNA repair in these regions." "Based on the result of our study, we found that gene regions, especially for the most biologically essential genes, are wrapped around histones with particular chemical marks," Monroe said. This signaling is not done by the DNA itself but by histones, specialized proteins DNA wraps around to make up chromosomes. Researchers found that to protect themselves, essential genes send out special signals to DNA repair proteins. The result is that offspring have a lower chance of inheriting a harmful mutation." "Our results show that genes, and essential genes in particular, experience a lower mutation rate than non-gene regions in Arabidopsis. "In genes coding for proteins essential for survival and reproduction, mutations are most likely to have harmful effects, potentially causing disease and even death," Monroe said. The non-random pattern in mutations between gene and non-gene regions of DNA suggests that there is a defensive mechanism in place to prevent potentially disastrous mutations. However, the researchers suspect that the level of non-randomness among different species may not be the same. "We have actually been following up with our study by investigating this question in other species and are finding results that suggest non-random mutation is not unique to Arabidopsis." ![]() "We think it is likely that other organisms could also have non-random genetic mutations," Monroe said. (Image credit: Pádraic Flood) (opens in new tab) Thale cress ( Arabidopsis thaliana) is a "model organism" for studying genetic mutations because of its small genome and short lifespan. But when they analyzed these mutations, they found that the parts of the genomes containing genes had much lower rates of mutation than non-gene regions. In total, the researchers sequenced 1,700 genomes and found more than 1 million mutations. Over three years, the researchers grew hundreds of plants in laboratory conditions for multiple generations. It also has a very short life span, which means that mutations can rapidly accumulate across multiple generations, Monroe said. Thale cress is a "great model organism" for studying mutations because its genome has only around 120 million base pairs (for comparison, the human genome has 3 billion base pairs), which makes it easier to sequence the plant's DNA. In the new study, researchers decided to test the randomness of mutations by investigating whether mutations were happening evenly between gene and non-gene regions of DNA in the genomes of thale cress. Most of the human genome is made of non-gene DNA, Monroe said. Mutations cause major changes to an organism only when they occur in genes - sections of DNA that code for a particular protein. Not all mutations have the potential to alter an organism's chances of survival. Germline mutations are what fuel evolution by natural selection and become more or less common in a population based on how they affect the carrier's ability to survive. There are two main types of mutations: somatic mutations, which cannot be passed on to offspring, and germline mutations, in which offspring can inherit the DNA error from a mutated gene in a parent. "If damage or copying errors are not repaired, they cause a mutation, a change in the DNA sequence," Monroe said. However, DNA repair proteins are not a foolproof solution and cannot fix all mistakes. "Our cells are working constantly to correct DNA and have evolved complex molecular machines, DNA repair proteins, to search for mistakes and make repairs," Monroe said. Luckily for humans and all other organisms, our cells can counteract a lot of this damage. "DNA also has to be copied each time a cell divides, which can introduce copying errors." ![]() "DNA is a fragile molecule on average, the DNA in a single cell is damaged between 1,000 and 1 million times every day," Monroe said. ![]() There are plenty of chances for genetic mutations and even errors to occur during the life of an organism. But the study does show that these genetic alterations are more complex than scientists previously believed. The new finding does not disprove or discredit the theory of evolution, and the researchers said randomness still plays a big role in mutations. "Even as a practicing geneticist and evolutionary biologist, I had never seriously questioned the idea." "The idea of random mutation has been around for over a hundred years in biology and is something you hear so often as a student that it is easy to take it for granted," Monroe said.
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