Table 2.

Nonsynonymous (d_N) and synonymous (d_S) substitutions (± standard error) as well as their ratio in ABS and non-ABS assuming concordance with the human MHC I and MHC II-DRB sequences (Bjorkman and Parham 1993; Brown et al. 1993).

MHC	Region	Sites	N	dN	dS	dN/dS	P
Class I	Exon 2	ABS	18	0.23 ± 0.08	0.08 ± 0.06	2.87	<0.01
		Non-ABS	65	0.04 ± 0.01	0.04 ± 0.02	1.00	0.71
		All	83	0.08 ± 0.02	0.05 ± 0.02	1.60	0.04
	Exon 3	ABS	16	0.18 ± 0.07	0.15 ± 0.13	1.20	0.51
		Non-ABS	71	0.02 ± 0.01	0.13 ± 0.04	0.15	<0.01
		All	87	0.05 ± 0.01	0.13 ± 0.03	0.38	0.02
Class II-DRB	Exon 2	ABS	24	0.21 ± 0.05	0.15 ± 0.08	1.40	0.35
		Non-ABS	58	0.04 ± 0.01	0.13 ± 0.05	0.31	0.06
		All	82	0.09 ± 0.02	0.13 ± 0.04	0.69	0.25

NOTE.—N is the number of codons in each category. P is the probability that d_N and d_S are different using a t-test.