In evolution, the role of chance has been re-evaluated thanks to "cannabis"

In evolution, the role of chance has been re-evaluated thanks to “cannabis”

What is evolution? Often described as a process that combines variation and selection, randomly occurring mutations in an individual’s genome affect their ability to ensure offspring in a given environment. Organisms may be the fruit of a genetic lottery that passes through the harsh filter to choose the most suitable—or at least from the most adequately fit. Biology textbooks insist on the central role of chance in the process of variation. But perhaps in light of the work on an unpretentious plant that became a laboratory model, Rashad Ms.Arabidopsis thaliana), this presentation should be improved.

Detlev Weigl, of the Max Planck Institute for Developmental Biology, in Tübingen (Germany), coordinated an international team presentation, at temper nature 13, that there are biases in the mutations observed in the genome of this fetish plant: the rate of their occurrence is already twice as low within genes – the so-called “coding” part of the DNA – just near them, and it is lowest for those that They encode proteins essential for cell function and reproduction.

Because of natural selection, which favors the most adapted individuals, the DNA sequence differences observed in nature only provide very incomplete information on potential mutation rate biases along the genome. So Detlev Weigl and colleagues developed a rigorous experimental protocol using a classic genetic tool, the Mutation Accumulation Lines. They grew in the lab 107 strains of Arabis, a self-fertilizing plant, over 24 generations, each time planting one seed (selected at random) per line and per generation. In this way, they eliminate every possibility of selection, except for mutations that produce nonviable or sterile individuals. at 25e generation, they sequenced the genome and thus identified all mutations accumulated in each line during 24 reproductive cycles.

Not completely random

Mutations observed in the population The ones that differentiate your genome from mine, for example It is the result of three stepsDetails: Detlef Weigel. Damaged DNA. DNA is not repaired properly; Selection and other factors determine whether this mutation “will survive”. With our protocol, there is so little selection that we see nearly all mutations as they arise. » Remarkably, the differences in the observed mutation rates are consistent with the genetic differences also observed in the natural populations ofArabidopsis : More polymorphisms in the DNA segment that confer a form of adaptive plasticity in the face of changes in the environment, and fewer mutations in genes central to plant metabolism.

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