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Genes code for 20 different amino acids that occur in proteins. There's genetically combinatorially room for more (64, right?) and hundreds of different (today abiotic) amino acids are chemically possible. Is there any evidence or theory about how the number and relative frequency of different proteinogenic amino acids in the biosphere has changed throughout the evolution? For example, have they increased slowly or suddenly or has there been these 20 of them for as long as can be determined?

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  • $\begingroup$ The so-called “universal” genetic code was elucidated for the bacterium E. coli. Based on several different types of evidence, that code table seems to hold true for all extant life forms on earth. From this observation we can infer that the last common ancestor of all life on earth also used this genetic code table (parsimony). If one of these codons specified a different amino acid (i.e., NOT on of the 20 canonical a.a.’s) in the past, where do you imagine that evidence would come from? $\endgroup$ – mdperry Dec 23 '18 at 0:39
  • $\begingroup$ @mdperry I expect the evidence to come from some biologist who works overtime on Christmas Day, together with Santa Clause ;-) So evolution hasn't had any evident impact on the assortment of amino acids used? $\endgroup$ – LocalFluff Dec 23 '18 at 8:39
  • $\begingroup$ What efforts have you made to answer this question yourself? A search for "evolution of the genetic code" would lead you to many papers and reviews on this topic. You would have quickly found the information @mdperry gave in his comment, as well as that there are theories that the 20 amino acids in the genetic code of the last common answer was preceded by a genetic code with a smaller number of amino acids. In the terms of SE Biology you should read some of these latter papers and then come back with specific questions. At the moment the question is far too broad for this list. $\endgroup$ – David Dec 23 '18 at 10:50
  • $\begingroup$ The "answer" is not obvious to me, because, as I said, the question is one of theory, not fact. What I said is that it was very broad or wide, one of the grounds for suggestng it be put on hold. I had assumed that you were aware how one should ask questions on this list, but let me now quote from the help on asking good questions "Have you thoroughly searched for an answer before asking your question? ... This demonstrates that you’ve taken the time to try to help yourself." Please delete your comment. It violates the code of conduct. $\endgroup$ – David Dec 23 '18 at 14:40
  • $\begingroup$ To be unambiguous regarding my intentions, I was emphatically NOT attempting to answer this question (that is why I made a comment). If I were going to answer the OP’s question I would have used the answer text area. The question that I posed in my comment was intended to underscore that we have no fossil evidence for protein sequences from billions of years ago. Even if we did have DNA sequence from a long-dead fossilized organism, in the absence of protein sequence data we have absolutely no way of determining if any of the 64 codons ever encoded a non-canonical amino acid. $\endgroup$ – mdperry Dec 24 '18 at 5:05

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