The Selecton server enables detecting the selective forces at a single amino-acid site. The ratio of non-synonymous (amino-acid altering) to synonymous (silent) substitutions, known as the Ka/Ks ratio, is used to estimate both positive and purifying selection at each amino-acid site
T. Risse, S. Dietze, D. Maynard, N. Tahmasebi, and W. Peters. Proc. of the Workhop on Detection, Representation, and Exploitation of Events in the Semantic Web (DeRiVE 2011), in conjunction with ISWC 2011, CEUR Workshop Proceedings Vol. 779, (2011)