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
S. Barrett. Data Mining and Text Mining for Bioinformatics:
Proceedings of the European Workshop, page 6--7. Dubrovnik, Croatia, (22 September 2003)Invited talk.