Purine-pyrimidine symmetry, determinative degree and DNA
  Various 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. 
Diana Duplij and Steven Duplij