Growth and reproduction complex in the rat. Genes linked to the major histocompatibility complex that affect development.

Abstract

The linkage of the major histocompatibility complex (MHC) and the growth and reproduction complex (Grc) in the rat was studied in an F2 hybrid population, generated from female BIL/1 (RT11-Grc) and male YO (RT1u-Grc+) animals: 1722 offspring were born, and 1568 were weaned and studied. The body weights of the offspring segregated with the RT1 haplotype of the MHC, and the RT11 homozygotes were significantly smaller than their RT11/u and RT1u/u littermates. The RT11/1 animals'' growth rate was approximately the same as that of the BIL/1 animals, and both were significantly less than the growth rates of the RT11/u, RT1u/u, and YO (RT1u) animals. The testes of the RT11 animals showed spermatogenesis arrest at the primary spermatocyte early pachytene stage; they were .apprx. 1/10 as heavy as the testes of the RT11/u and RT1u/u animals. The ovaries in females of all 3 haplotypes had the same weight, but there was a decrease in the ova number released/cycle in the RT11/1 animals. The major RT11 homozygote loss, which caused distortion of the phenotypic ratios among the offspring, did not occur in utero but in the early postnatal period before weaning. There were 7/1568 recombinants between the MHC, using the RT1.A antigen as the marker and the Grc, using small body size (dw-3) as the marker, and 1/1568 recombinant between the loci influencing body size (dw-3) and fertility (ft) of the Grc. These data gave the following map distances (95% confidence levels): RT1.A to dw-3, 0.45 (0.25-0.96) centimorgans and dw-3 to ft, 0.07 (0.04-0.40) centimorgans. A female recombinant was used to develop an inbred line carrying the RT1.A1-Grc+ chromosome.