PROPERTIES OF A GENERAL-MODEL OF DNA EVOLUTION UNDER NO-STRAND-BIAS CONDITIONS

Under the hypothesis of no-strand-bias conditions, the Watson and Cric k base-pairing rule decreases the complexity of models of DNA evolutio n by reducing to six the maximum number of substitution rates. It was shown that intrastrand equimolarity between A and T (A T*) and betwee n G and C (G C*) is a general asymptotic property of this class of mo dels. This statistical prediction was observed on 60 long genomic frag ments (>50 kbp) from various kingdoms, even when the effect of the two opposite orientations for coding sequences is removed. The practical consequence of the model for estimating the expected number of substit utions per site between two homologous DNA sequences is discussed.