Mutations may not arise by chance

The basic assumption about the origin of mutations, and therefore about evolution, may be wrong. It appears that the new mutations in the genome were not distributed randomly, according to a report by a team led by J. Gray Munro and Detlev Weigl (Max Planck Institute for Biology, Germany) in temper nature. From a complete overview of newly formed changes in the cress DNA (Arabidopsis thaliana), it has been shown that half the number of mutations that occur in genes is half the number of mutations in the rest of the DNA. Two-thirds fewer new changes occurred in the genes necessary for the plant to function. Until now, specialists assumed that mutations appear randomly in the genome and disappear only in subsequent generations through natural selection of important genes.

The team examined the genomes of 400 different cress breeds to look for mutations that originated in individual plants and have not yet undergone natural selection. Biologists have cataloged each of the new mutations in Kimban In seeds, the so-called somatic mutations that arose over the life of plants. The first analysis has already shown that some parts of DNA are more sensitive to mutations.

The team then linked the frequency of mutations in a specific DNA segment to its physical and chemical properties, such as epigenetic changes in the DNA itself or in the DNA. histone, the frequency at which each Nucleus It occurs or how accessible this part of the DNA is from the outside. These factors ensure that mutations are not random, at least they are the Suspect. In fact, it turns out that in the parts with very few mutations, there are certain factors prevent that promote highly effective repair of DNA damage, such as epigenetic changes in histones.

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A large proportion of the nucleobases cytosine and guanine It makes DNA more chemically stable. volatile On the other hand, cytosine is more susceptible to chemical changes that lead to mutations. So the researchers found higher proportions of methylated cytosine in regions with more mutations. Moreover, the easily accessible structure of DNA hampers the repair enzymes, so that mutations often occur in those places. It is often access to regulatory regions that initiate gene transcription, eg regions to which transcription factors bind. On the other hand, the genes themselves turned out to be significantly more stable.

While many of these effects were already known, their effect on the spread of new mutations is surprising. Researchers believe that the difference in the stability of certain parts of the DNA itself is the result of natural selection. It is a clear evolutionary advantage if the genes essential for survival are more stable. However, it is still not clear why the entire genome is not as stable as possible. Some important characteristics of parts of DNA may hinder greater stability. But the natural variation between offspring, caused by differences in gene regulation through random mutations, can also be itself an evolutionary advantage.

This article previously appeared in Domain.

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