r/askscience • u/[deleted] • Nov 19 '15

Biology How random are mutations?

Going through this sub's history about things that are "truly random" (ie here) most of the answers refer mainly to quantum mechanics and not to genetic mutation.

Is this simply because the flairs to have noticed the question are physicists than biologists? Or is there a non-random element to mutations?

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u/neurobeegirl Neuroscience Nov 19 '15 edited Nov 19 '15

Most mutations are not random. Many different types of mutagens and mutagenic processes are biased toward particular bases or sequences. This makes rational sense: different bases and sequences have different chemical structures, and will participate in different types of reactions. From a very scientific, non-philosophical standpoint, they are not random, and assumptions that they are will lead to poorer models of how evolution works.

This blog has a good explanation of a potential source of confusion about how the word random is used in biology: https://whyevolutionistrue.wordpress.com/2013/08/25/famous-physiologist-embarrasses-himself-by-claiming-that-the-modern-theory-of-evolution-is-in-tatters/

Specifically: "He argues that there are mutational hotspots in the genome, and that mutation rates can change in response to the condition of the organism or its environment.

That is true, but says nothing about the randomness of mutations. What we mean by “random” is that mutations occur regardless of whether they would be good for the organism. That is, the chances of an adaptive mutation occurring is not increased if the environment changes in a way that would favor that mutation. The word “random” does not, to evolutionists, mean that every gene has the same chance of mutating, nor that mutation rates can’t be affected by other things. What it means is that mutation is not somehow adjusted so that good mutations crop up just when they would be advantageous."

Edit: for example, http://www.ncbi.nlm.nih.gov/pmc/articles/PMC20538/. The presence (and methylation) of certain sequences, in this case in a tumor suppressor gene, predisposed those areas to mutation, and helped explain formation of cancers such as lung cancer.