Except some organisms, most organisms follow the same Genetic Code

tRNAs, tRNA synthetases, ribosomes, etc. comprise the translational machinery for converting nucleotide codons to proteins.

My question is:

Why is the genetic code so heavily conserved across life, given that the genes for the translational components noted above presumably vary significantly across evolution?

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    $\begingroup$ Can you cite any sources or point to anything that indicates where you got your information? Note that the genetic code is not the same for all organisms: en.wikipedia.org/wiki/Genetic_code#Alternative_genetic_codes $\endgroup$ Dec 14, 2021 at 18:37
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    $\begingroup$ I suggest that you read more about the evolution of translation and transfer RNAs, they are not stable in their sequence (e.g. frontiersin.org/articles/10.3389/fgene.2014.00303/full). While in general the genetic code and the translational apparatus is remarkably conserved (and therefore a good argument for a single origin of life), it is by no means "frozen" or identical across all organisms. $\endgroup$ Dec 14, 2021 at 19:11
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    $\begingroup$ tRNAviz is a neat tool from the Lowe lab that allows you to visualize the structure and sequence variation of tRNA isotypes across the tree of life. $\endgroup$
    – acvill
    Dec 14, 2021 at 19:18
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    $\begingroup$ @acvill that link seems to be broken, this one works: trna.ucsc.edu/tRNAviz/summary $\endgroup$ Dec 15, 2021 at 18:12
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    $\begingroup$ I suggest you reflect on what happens if a single mutation occurs in a gene during evolution. There is a chance that it can be lethal, beneficial or neutral. Now, how many mutations would occur in a bacterium of 1000 genes if a mutation of the anticodon of a tRNA caused the wrong amino acid to be inserted everywhere it occurred? And what effect would that have? So the question — which is not easy to answer — is really, how did the alternative genetic codes ever evolve? $\endgroup$
    – David
    Dec 15, 2021 at 21:20

1 Answer 1


There are a variety of posts on this site already that address related questions:

I don't believe that any of these answers specifically address the high conservation of the code, except as implicit (though I could be missing something).

A useful paper

However, one such post links to this paper that discusses the evolution of the genetic code.

Part of the introduction restates the question's motivation rather well, I think:

The fundamental question is how these regularities of the standard code came into being, considering that there are more than $10^{84}$ possible alternative code tables if each of the 20 amino acids and the stop signal are to be assigned to at least one codon.

In other words, why has this space of $10^{84}$ codes not been more widely explored than we observe in nature?

The first part of the paper's abstract seems relevant (I have bolded a few sections that might be taken as explanatory hypotheses):

The genetic code is nearly universal, and the arrangement of the codons in the standard codon table is highly non-random. The three main concepts on the origin and evolution of the code are the stereochemical theory, according to which codon assignments are dictated by physico-chemical affinity between amino acids and the cognate codons (anticodons); the coevolution theory, which posits that the code structure coevolved with amino acid biosynthesis pathways; and the error minimization theory under which selection to minimize the adverse effect of point mutations and translation errors was the principal factor of the code’s evolution. These theories are not mutually exclusive and are also compatible with the frozen accident hypothesis, i.e., the notion that the standard code might have no special properties but was fixed simply because all extant life forms share a common ancestor, with subsequent changes to the code, mostly, precluded by the deleterious effect of codon reassignment.

They then review a variety of evidence for each theory, from which I will present one example.

Is the genetic code optimal?

They note a 1991 paper that used biophysical properties of amino acids and estimated that a randomly selected genetic code was ~0.01% likely to be at least as robust as the existing genetic code. In other words, the code seems to have at least somewhat minimized possible errors. So, the existing code is at least well above-average in terms of possible codes, and it's possible that the reason no better codes have been explored is that it's trapped in a local minimum of the code landscape (see Figure 3 from that paper here).

Figure 3 from Koonin and Novozhilov 2012, showing possible genetic code adaptive landscape.

They go on to discuss this in more detail. I personally find other evidence about the "coevolution" and "collective evolution" theories interesting, but obviously it is hard to repeat a multibillion year experiment.


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