We report on the search for symmetries in the genetic code involving the medium rank simple Lie algebras B 6 = so(13) and D 7 = so (14), in the context of the algebraic approach originally proposed by one of the present authors, which aims at explaining the degeneracies encountered in the genetic code as the result of a sequence of symmetry breakings that have occurred during its evolution. Work supported by CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) and by FAPESP (Fundação de Amparoà Pesquisa do Estado de São Paulo), Brazil. 3135 Int. J. Mod. Phys. B 2003.17:3135-3204. Downloaded from www.worldscientific.com by ROYAL INSTITUTE OF TECHNOLOGY on 02/03/15. For personal use only. 3136 F. Antoneli et al.to allocate the aminoacids and the termination signal. This process of spontaneous symmetry breaking has been used before, in various fields of science. The crucial point in such a search for symmetries is to find the ancestor group G and the possible chains of subgroups. The first search for symmetries in the genetic code along this line of reasoning, as outlined in Ref. 1 (see also Ref. 2, and Refs. 3 and 4 for comments), has been carried out within the class of ordinary compact Lie groups G or, what amounts to the same thing, of semisimple Lie algebras g, based on Cartan's classification of semisimple Lie algebras, Dynkin's classification of their maximal semisimple subalgebras 5,6 and the tables of branching rules of McKay and Patera. 7 This search has shown that, on the one hand, there is no simple Lie algebra that can generate the standard genetic code directly in its present form. On the other hand, it turned out that the standard genetic code can be obtained from the symplectic algebra sp (6) if, in the last step, the process of symmetry breaking is allowed to be gently interrupted, or frozen. This means that a few of the multiplets (subspaces) that have resulted from previous steps of the process do not participate in the symmetry reduction implied by the last step.Two restrictions have been imposed on the search reported in Ref. 1. The first refers to the last phase of the process, after the ancestor algebra has already been broken to a direct sum of su(2)-subalgebras. In this last phase, further steps consist in breaking one or several of these su(2)-subalgebras completely, which in the language of atomic or nuclear physics can be implemented by introducing an appropriate generator L z into the Hamiltonian. Another possibility that was also considered is to introduce instead its square L 2 z , which leads to a softer form of symmetry breaking. However, the possibility of performing both of these breakings sequentially, with freezing applied to the second step only, was not contemplated. The second restriction was the exclusion of "diagonal breaking", which in the case of su(2)-subalgebras amounts to a Clebsch-Gordan summation law for quantum numbers.In Ref. 8, this search has been enlarged as a consequence of a new geometric interpretation of the operator L 2 z (rather than L z )...