Evolution within the multigene family coding for the class I histocompatibility antigens: the case of the mouse t-haplotypes.

The t-haplotypes of the house mouse are defined by several genetic events which involve about one-third of chromosome 17 and include the major histocompatibility complex (MHC). One of the primary features of complete t-haplotypes is the nearly complete suppression of recombination between a t-chromosome and a wild-type chromosome 17. If we assume that all genetic exchanges are abolished because of the inhibition of recombination, the class I genes of the MHC can be used as vicinity markers of t-haplotypes. We have studied the H-2K, D and L genes of 10 independant t-haplotypes and have found that their H-2K genes are rather polymorphic, although always very similar or identical to H-2K genes of laboratory mice. By contrast, the DL-Tla region is nearly constant. It is suggested that the t-haplotypes reveal the existence of several mechanisms involved in the evolution of the MHC, one of which is possibly the greater "mobility" of H-2K genes in the genome.