Gene order in the major histocompatibility complex of the rat

The loci in the major histocompatibility complex (MHC) of the rat which code for class I and class II antigens--RT1.A and RT1.B, respectively--have previously been separated by laboratory-derived recombinants and by observations in inbred and wild rats. Closely linked to the MHC is the growth and reproduction complex (Grc) which contains genes influencing body size (dw3) and fertility (ft). These phenotypic markers were used in this study to orient the A and B loci of the MHC. Two recombinants were used for mapping. The BIL(R1) animal is a recombinant between the MHC and Grc, and it carries the haplotype RT1.AlBlGrc+. The r10 animal is an intra-MHC recombinant, and it has the haplotype RT1.AnB1Grc. These recombinants were characterized serologically, by mixed lymphocyte reactivity, by immune responsiveness to poly (Glu52Lys33Tyr15) and by the presence of the dw-3 gene. The data demonstrate that the gene order of the loci is: dw-3--RT1.B--RT1.A.