Selective constraints on the six species of the melanogaster group of Drosophila. Numbers above branches (in red) show the estimates of the ω parameter (ω = nonsynonymous substitution rate [dN]/synonymous substitution rate [dS]). Numbers below branches indicate the dN (in black) and dS (in blue) values, respectively. The ω values were calculated applying the free ratio (FR) model on the concatenated multiple alignment (set of 42 orthologous groups).
Vieira et al. Genome Biology 2007 8:R235 doi:10.1186/gb-2007-8-11-r235