Figure 1.

Southern blot analysis of intra-MHC recombinants suggests that, in contrast to mammals, the Xenopus MHC class Ia gene is associated with the class II region. (a) Southern blotting analysis of class IIβ (10), lmp7 (16), class Ia (9), C4 (14), Bf (12), and HSP70 (15) genes using DNA from 17 members of an r/f × r/f cross. Probes detected an intra-MHC recombinant (animal #3). The r/r and f/f lanes display the hybridization patterns of the f and r MHC haplotypes (DNA obtained from MHC homozygotes). (b) Order of Xenopus MHC genes based on recombinants (barring double crossovers) detected in pedigree analyses. In previous tying of members of an f/f × f/g family, recombinant offspring #15 displayed cosegregation of class II and lmp7 on the one hand and class Ia, C4, Bf, C4, and HSP70 on the other (16). The recombinant haplotypes noted below are derived from the animal in Fig. 1a. Vertical bars indicate genes. Doubleheaded arrows show that the order of the indicated loci is unknown and may be reversed. Note that the number of HSP70 genes may be two or three (15).