TABLE 1

Divergences of orthologous odorant-receptor genes in rat and mouse

OrthologsRaw differencesEstimated substitutions
RatMousecdnd1d2d3aaaa/cdKS(SD)KA(SD)KA/KS
NORs
mK20rmK20m8691990.1050.12(0.042)0.048(0.0164)0.39
rF12rrF12m265171646320.121*0.23(0.039)0.066(0.0112)0.28
rI8rrI8m267251759400.150*0.32(0.046)0.078(0.0120)0.25
rI9rrI9m26212833190.0730.18(0.033)0.035(0.0080)0.20
mK7rmK7m133421760.0450.17(0.045)0.024(0.0092)0.14
mM31rmM31m89511970.079*0.32(0.082)0.037(0.0142)0.12
rF6rrF6m263463480.0300.17(0.030)0.017(0.0058)0.10
rI7rrI7m270612450.0190.13(0.026)0.009(0.0041)0.07
All sequences163582522411260.0770.20(0.014)0.040(0.0034)0.20
KS ≤ 0.210143518117470.0460.16(0.015)0.023(0.0033)0.15
TORs
rT19rmT18m11212516190.170*0.24(0.074)0.075(0.0177)0.32
rT07rrT07m12642850.0400.08(0.028)0.019(0.0086)0.24
mT09rmT09m268191050240.092*0.27(0.041)0.050(0.0096)0.18
rT09rrT09m261943790.0340.19(0.033)0.020(0.0058)0.11
rT44rmOR3m157331950.0320.17(0.042)0.018(0.0076)0.10
mT15rmT15m13311720.0150.13(0.036)0.010(0.0060)0.08
rT05rmT07m157212030.0190.16(0.038)0.009(0.0054)0.06
mT33rmT33m264623840.0150.20(0.034)0.009(0.0041)0.04
rT38rmT53m15732120.0130.20(0.048)0.008(0.0045)0.04
rT18rrT18m2633310.0000.18(0.034)0.002(0.0018)0.01
All sequences18986227257730.0380.19(0.012)0.020(0.0023)0.11
KS ≤ 0.215183112191300.0200.17(0.013)0.011(0.0019)0.07

The length of each aligned sequence pair is given in codons (cdn), with differences at first, second, and third positions (d1, d2, d3), and the number (aa) and proportion (aa/cd) of amino acid differences. Estimated synonymous substitutions per synonymous site (KS) and nonsynonymous substitutions per nonsynonymous site (KA) are given with their standard deviations. KS is highly variable (sKs = 0.064), and KS and KA are correlated over these 18 gene pairs (r = 0.57), as they are for other pairs of putative orthologs in rat and mouse (Wolfe and Sharp 1993; Makalowski and Boguski 1998).

  • * the five KS values >0.2 [slightly less than one standard deviation above the mean for hundreds of rat-mouse orthologs (Makalowski and Boguski 1998)]; most analyses are performed both with and without these homolog pairs, which are presumably the ones at greatest risk of being paralogous. The ratio KA/KS estimates the probability of fixation for a nonsynonymous (amino acid changing) mutation, relative to the probability for a synonymous mutation, and therefore indicates the apparent efficiency with which selection resists amino acid substitutions (smaller values of KA/KS indicating more stringent selection). The 10 TOR sequences combined show a KA/KS ratio 55% as large as for the 8 NORs (47% as large for genes with KS ≤ 0.2). The overall KA for TORs is 50% as large as for NORs (48% as large for genes with KS ≤ 0.2), and TORs show 49% as many amino acid differences per codon (43% as many for genes with KS ≤ 0.2).