2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/83760Various symmetries connected with purine-pyrimidine content of DNA sequences are studied in terms of the intruduced determinative degree, a new characteristics of nucleotide which is connected with codon usage. A numerological explanation of CG pressure is proposed. A classification of DNA sequences is given. Calculations with real sequences show that purine-pyrimidine symmetry increases with growing of organization. A new small parameter which characterizes the purine-pyrimidine symmetry breaking is proposed for the DNA theory.8 pages, Latex 2e, amsmath, amssymbBiological PhysicsMathematical PhysicsGenomicstext