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Junk DNA and “random” mutations

Junk DNA and “random” mutations


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I'm somewhat irritated by "mutation" generally being described as a fully random factor in evolution: pure randomness does not seem like something that can survive in a long evolutionary process.

And some basic evolution in some long-lived organisms appears to happen in quite fewer generations than one would consider plausible considering just natural selection over an unbiasedly mutated genetic base.

So I'm wondering whether there have been attempts to view mutation itself as a process influenced by evolution. For example, couldn't "junk DNA" result in a susceptibility to certain mutations that is determined by environmental factors, like amount and constitution of nutrients, ambient temperatures and others.

The overall discussion of mutagenesis I can find focuses entirely on "damage", again basically assigning all mutations a negative or at least undirected character (like more mutations occuring under stress, with the "aim" being more likely to have more random mutations where one offspring might be more successful than the stressed parent by chance).

In a similar vein, I don't see not much of anything about evolution and competition of gametes: how different environmental factors influence which of an abundance of eggs mature and which of the (asexual) male gamete reproduction mutation in the testes will be favored over time or under environmental conditions.

Basically all of evolution and natural selection seems about how to survive into fertility and select a partner, and that's it as genes are constant apart from random cosmic radiation or toxic substances.

I think that this kind of viewing the message in the DNA as isolated from its medium just does not sound like something that would survive billions of years without something less random replacing the pure randomness.

So are there any major studies trying to figure out whether certain mutations leading to better adapted phenotypes occur in a non-random manner (namely not just affecting mutation rate but also direction) in response to environmental circumstances?


pure randomness does not seem like something that can survive in a long evolutionary process.

I think this is because you don't quite understand (no offense) the interplay between mutations and natural selection. You should have a look at Understanding Evolution.

The overall discussion of mutagenesis I can find focuses entirely on "damage"

This is because the vast majority of mutations are deleterious (=damaging). But obviously, not all mutations are deleterious, otherwise no adaptation would be possible (only purifying selection would occur).

In a similar vein, I don't see not much of anything about evolution and [… ]

I don't understand this paragraph.

Basically all of evolution and natural selection seems about how to survive into fertility and select a partner [… ]

No! There is much more to evolution than that. Note that the semantic of evolution and natural selection is wrong as they are used in your sentence. Again, check out an introductory course.

I think that this kind of viewing the message in the DNA as isolated from its medium

No! The environment is a fundamental tenet in evolutionary biology. The association between genotypes to fitness is a function of the environment as well.

Are mutations random?

The mutation rate varies dramatically among species and along genomes (roughly speaking from $10^{-2}$ to $10^{-10}$). For example microsatellites (repeated sequences) are highly mutable. Note also that the probability of a given nucleotide to mutate depends also on the exact nucleotides that are around it (Rob Ness; Personal communication). The mutation rate is also a plastic trait (and is therefore under selection) in some species (of plants typically). The environment affect the mutation rate and the environment can be chosen by some species (avoidance) or even constructed in some species (niche construction). In multicellular organisms, the age of the father correlates with the number of new transmitted mutations as well. However I have never heard of any studies showing such behaviours in order to affect the mutation rate. Epigenetic changes (does not concern all species) can also the mutation rate and even into what new nucleotide the old nucleotide will be mutated into (with a given probability). Mutations are more likely to be transitions than transversions. If a specific region is under environment-depend selection, then a mutation that would allow to drastically increase the mutation rate at this nucleotide whenever the organism has a low fitness (or even whenever the trait of the organism is unfit for the specific environment) could reach fixation. This process (and maybe others I am not aware of) are I think encapsulated within a hypothesis called (and it is a horrible name as it can yield to confusion) adaptive mutation hypothesis. But really don't start studying any field of science by jumping into an advanced subject (or even worst, a controversial subject). You should start with an introduction.

However, the impact on fitness (and on phenotype) of a new mutation is essentially random. An organism has absolutely no way to know what protein will be caused by a given new mutation. Selection then select upon the variance created by the mutations, the variance decreases and adaptation occurs. The impact of new mutations seem to follow more or less two weighted gamma distributions (added to which a bump of probability density for lethal mutations).


Did you hear about the historical Luria-Delbrück experiment where they demonstrated that in Escherichia coli mutations conferring resistance to antibiotics are essentially random?

Also, discussions and some references on the phenomenon of (directed) adaptive mutagenesis, which I think you are asking about, is mentioned in the Wikipedia article. But I don't know much about the debate.


Watch the video: Junk DNA: Susumu Ohnos original paper (May 2022).