  Why is the genetic code the way it is? The most successful theory states that
the codon assignments minimise the effects of errors arising in primordial
living systems. Here a transversion is reported that leaves invariant
degeneracy in the genetic code. A model was established to address the
question: How should sets of synonymous codons be chosen to minimise the
deleterious effects of non synonymous substitutions? It is shown that the
arithmetic theory of quadratic forms provides the framework for degeneracy in
the genetic code.
