particular amino acid belongs to a given selection class
(neutral, conserved or highly variable). Sites with greater
posterior probability (PP C 95 %) of belonging to the
‘x[1 class’ were inferred to be positively selected.
Single Likelihood Ancestor Counting (SLAC), fixedeffects
likelihood (FEL) and random-effects likelihood
models (Kosakovsky Pond et al. 2005) implemented in