Genetic mutations, not completely random?
This is the opposite of the conclusion in the current textbook.
Remember the white-eyed fruit flies, white-haired calves, or giraffes or brachyces in middle school biology textbooks?
In these examples, mutations are either artificially caused by the outside world or are completely random, and only natural selection can determine which mutations appear in the organism.
But now, a new paper published in Nature makes this subversive point with the results of the experiment:
The region of the genome where mutations occur has obvious regularities and is not completely random!
For example, in the region of the essential gene that is decisive for survival, the mutation rate drops by almost 2/3.
This behavior, which approximates the "subjective control" of genetic mutations by organisms in order to survive, is completely contrary to the natural selection of natural selection and random mutations mentioned above.
Now, the study has not only shaken the research community, but also sparked a lively discussion on Twitter:
And this subversive conclusion is also linked to the use of Ramackism.
Some netizens even asked directly:
Is this to rehabilitate Lamarckism?
Find the answer from the plant Arabidopsis
The paper was written in collaboration with two institutions, the University of California, Davis, and the Max Planck Institute in Germany, which are not generalists.
To figure out the deep laws behind genetic mutations, scientists spent 3 years studying more than 1 million genetic mutations.
All of the mutation data came from a plant called Arabidopsis thaliana, which scientists refer to as "fruit flies in plants."
This plant is an ideal material for genetic research due to its small plant size, many fruits, short life cycle, simple genome, and simple genetic manipulation (compared to the 3 billion base pairs of humans, it has only 120 million).
The plants are cultivated in a laboratory setting, and by the 25th generation, there are already 40 seedlings per strain.
These seedlings were then sampled as they reached the four-leaf stage of 2 weeks of age, and genetic mutation points were found and analyzed using gene data analysis software (GATK HaplotypeCaller12).
Surprisingly, in these mutations, the scientists found that the pattern was not quite the same as expected.
Specifically, mutation rates in some specific regions of the genome are significantly lower: more than 50 percent lower than other regions.
In these regions with lower mutation rates, the scientists found that essential genes, which are mainly related to cell growth and gene expression, have dropped their mutation rates by 2/3.
This means that DNA mutations are not random.
As for why the probability of gene mutation is different at different locations, the authors do not give the fundamental reason -
Whether this piece of DNA itself is not easy to mutate, or whether the later DNA repair is particularly effective for this section, is not known.
But this result still poses a new challenge to Darwin's theory of evolution, which is regarded as the standard.
In addition, the scientists have found that by the type of protein that wraps dna, it is possible to predict which genes are more likely to mutate than other genes.
The impact of this finding is also exciting.
Because once you master the method, you can use genetic mutations to grow better crops, and you can also help scientists develop new ways to treat cancer caused by mutations.
Question: Survivor bias?
The paper's corresponding author is J. Grey Monroe, an assistant professor in the Department of Plant Sciences at the University of California, Davis, who graduated from Colorado State University with a Ph.D. in 2019.
His personal tweet of the publication of the research led to a very wide range of discussions, one of the most direct questions was:
How do you guarantee that this is not a survivor bias?
Here's a very classic "aircraft fuselage bullet hole" diagram that explains survivor bias:
Judging from the number of bullet holes in different positions on the fuselage, the wings that are the most seriously shot should be reinforced, while the cabin without many bullet holes is not needed. But in fact, hitting the cabin plane will crash directly, and there is no chance of coming back to be counted.
Behind this comment, the question is:
Experiments measure surviving individuals, and those mutant individuals who seriously endanger survival may not survive at all, so the results measured are non-fatal mutations.
Also, epigenomes involved in gene expression, individual development, and tissue differentiation may affect the "mutation rate" in experimental results.
Many commentators have made similar observations, arguing that the genome regions with lower mutation rates mentioned in the paper may be inherently conservative and not easily mutated regions.
For example, Conserved Sequences are specific sequences that are retained during evolution, are not easy to mutate, and can generally be pushed up to the early stages of species evolution.
And because the author himself proposes that our findings seem to contradict the existing theory that "the earliest mutations are completely random", some people have also thought of the famous "use in and out" theory in biology, asking:
Is this to rehabilitate Lamarck?
Lamarck is best known for his "use-in" view that the organs that organisms often use will gradually develop, and the organs that are not used will gradually degenerate.
In other words, first choose, then mutate.
In response, corresponding author Grey Monroe replied affirmatively in a follow-up conference document:
This is not the subject of this paper.
He said that the study only proved experimentally that in some cases, mutations are non-random and environmentally adaptable, which provides new evidence and ideas for the study of the evolution of life.
But Grey Monroe concludes by saying that historically , " mutations are random " is clearly an oversimplified assertion , or " a " bad hypothesis " , and he's glad the paper sparked a widespread discussion of the theory.