author | home
More than one codon specifies individual amino acids.
Because there are 64 possible combinations of four bases in three-nucleotide sequences, but (usually) only 20 amino acids that are translated, in order for most codons to be sense codons, that is, encoding an amino acid, then some of those amino acids must be specified by more than one codon. Indeed, most amino acids are specified by more than one codon such that only three of the 64 total codons are nonsense codons, that is, which specify instead stop codons. Compare with lack of ambiguity in the genetic code. See also lack of punctuation between codons.
The utility of a high degree of redundancy in terms of codon specificity, and associated relative dearth of stop codons within the total set of codons, are together useful towards increasing the potential for mutations to give rise to either neutral or beneficial alleles. Specifically, in mutationally changing from one allele to another, it is extremely helpful that the resulting allele, much more often than not, is going to specify some amino acid. Indeed, in a number of cases a mutation in a codon will not change what amino acid is encoded at all (i.e., see wobble).
Mutations, as a consequence, are themselves not inherently disastrous to the functioning of organisms. Yes, they can tend to result in a loss of functioning of gene products, but more often than not there nevertheless will still at least be a gene product and therefore something that evolution can quite literally work with.
For more on this topic, see Wikipedia and Google. Contact web master. Return to home.