- Mario Dos Reis: Department of Genetics, Evolution and Environment, University College London, Gower Street, London WC1E 6BT, UK mario.barros@ucl.ac.uk.
First principles of population genetics are used to obtain formulae relating the non-synonymous to synonymous substitution rate ratio to the selection coefficients acting at codon sites in protein-coding genes. Two theoretical cases are discussed and two examples from real data (a chloroplast gene and a virus polymerase) are given. The formulae give much insight into the dynamics of non-synonymous substitutions and may inform the development of methods to detect adaptive evolution.