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The balance of evidence both from the cell-free system and from the study of mutation, suggests that this does not occur at random, and that triplets coding the same amino acid may well be rather similar.

Unfortunately it makes the unambiguous determination of triplets by these methods much more difficult than would be the case if there were only one triplet for each amino acid.

Attempts have been made from a study of the changes produced by mutation to obtain the relative order of the bases within various triplets, but my own view is that these are premature until there is more extensive and more reliable data on the composition of the triplets.

A final proof of our ideas can only be obtained by detailed studies on the alterations produced in the amino acid sequence of a protein by mutations of the type discussed here.

It now seems very likely that many of the 64 triplets, possibly most of them, may code one amino acid or another, and that in general several distinct triplets may code one amino acid.

The meaning of this observation is unclear, but it raises the unfortunate possibility of ambiguous triplets; that is, triplets which may code more than one amino acid. However one would certainly expect such triplets to be in a minority.

This seems highly likely, especially as it has been shown that in several systems mutations affecting the same amino acid are extremely near together on the genetic map.

It now seems certain that the amino acid sequence of any protein is determined by the sequence of bases in some region of a particular nucleic acid molecule.

It has yet to be shown by direct biochemical methods, as opposed to the indirect genetic evidence mentioned earlier, that the code is indeed a triplet code.

Most mutations involve typos: Something bumps a cell's elbow as it's copying DNA, and the wrong letter appears in a triplet - CAG becomes CCG.