Table 1. Results of two-ratio model tests of selection pressure on the STRA6 gene in vertebrate.

Model	Np	l	ω 0 a	ωa	Model Compared	2Δl	P
A. One ratio: ω 0	177	−75502.66	0.24280	= ω 0
B. Free ratio	351	−75230.33			B VS. A	544.66	0
C. Two ratios: ω0, ωA	178	−75492.31	0.23709	0.32960	C VS. A	20.7	0.0000
D. Two ratios: ω0, ωB	178	−75486.85	0.23622	0.36393	E VS. A	31.62	0
E. Two ratios: ω0, ωC	178	−75500.15	0.24090	0.30001	F VS. A	5.02	0.0250
F. Two ratios: ω0, ωD	178	−75499.26	0.23764	0.26994	H VS. A	6.8	0.0091
G. Two ratios: ω0, ωE	178	−75499.95	0.24034	0.29153	J VS. A	5.42	0.0199
H. Two ratios: ω0, ωF	178	−75500.30	0.23986	0.27722	K VS. A	4.72	0.0298
I. Two ratios: ω0, ωG	178	−75483.61	0.25688	0.19305	M VS. A	38.1	0
J. Two ratios: ω0, ωH	178	−75484.24	0.25236	0.17541	N VS. A	36.84	0

a ω(ω_A, ω_B, ω_C, ω_D, ω_E, ω_F, ω_G, ω_H) and ω₀, are the ratios for branches A, B, C, D, E, F, G, H and other branches, respectively (see Fig. 1).