Five class II H-2 genes borne by t chromosomes were partially sequenced: [formula omitted] borne by the tTuw10 chromosome of EDY589 (H-2w2); [formula omitted] and [formula omitted] borne by the tTuw8 chromosome of CR0437 (H-2w57), as well as [formula omitted] and [formula omitted] borne by the tTuw7 chromosome of CR0435 (H-2w37). These genes are representatives of the three major groups of alleles found associated with t chromosomes. The sequenced part consisted of almost the entire exon 2 and the entire exon 3 coding for the first and the second domain of the β polypeptide chains, respectively. The sequence was compared with the published sequences of Aβ and Eβ alleles borne, by non-t chromosomes. The comparison revealed that the t-associated alleles are no more similar to one another than they are to the corresponding genes present on non-t chromosomes in laboratory mice. This divergence in the nucleotide sequence among the class II genes is interpreted as evidence that the t complex is very old.
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