The odorant receptor repertoire of teleost fish

BMC Genomics

Table 3 Comparison of selective pressure by transmembrane domain.

	TM1	TM2	TM3	TM4	TM5	TM6	TM7	non-TM	CDS
Length (amino acids)	26	21	19	24	25	19	24	110	268
Mean pairwise dN/dS ^a	0.330	0.276	0.457	0.574	0.437	0.513	0.282	0.304	0.325
TM vs loops p-value (2 -tailed t test) ^b	9.9E-04	0.81	2.1E-12	7.6E-21	1.2E-18	2.5E-10	1.00
TM vs CDS p-value (2 -tailed t test) ^b	0.45	0.025	2.1E-08	5.9E-16	7.9E-12	6.0E-07	0.0024
Number of positively selected sites (p < 0.1) ^c	0	0	1	1	0	0	0	2	4
Number of negatively selected sites (p < 0.1) ^c	21	16	12	15	15	14	19	80	192

^a The mean ratios of non-synonymous substitutions per non-synonymous site (dN) to synonymous substitutions per synonymous site (dS) were calculated for each transmembrane region, the aggregate of the non-transmembrane regions, as well as the entire OR coding sequence. dN/dS ratios were calculated only for pairwise comparisons in which mutational saturation had not been reached. A constant set of 262 informative pairs was used for all calculations.
^b Probabilities that the average dN/dS ratio for the particular TM domain is no different than the average for the entire CDS or the non-TM domains, using a two-tailed t test.
^c Number of sites with probabilities greater than 0.9 (p < 0.1) of being positively or negatively selected for each domain. Ancestral sequences were reconstructed, and at every non-constant site, dN and dS were calculated. If dN < (or >) dS, a p-value derived from a two-tailed binomial distribution was used to assess significance.

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