Heredity of the GIX thymocyte antigen associated with murine leukemia virus: segregation data simulating genetic linkage.

The GIX antigen is a feature of the gp70 envelope glycoprotein of murine luekemia virus (MuLV). This GIX-gp70 molecule is found on the thymocytes of some (GIX+) strains of mice, where its expression is controlled by two mendelian genes, Gv-1 and Gv-2. Previous recombination data involving the prototype GIX+ strain 129 indicated that the H-2 (chromosome 17) and Gv-1 loci are linked, at a distance of 36 units from one another. New data indicate that the association of H-2 and GIX phenotypes is an example of quasi-linkage, evidently dependent in this instance on heterozygosity at a locus or loci in the vicinity of H-2. Other previous recombination data, involving the GIX+ strain AKR, had indicated that the Gpd-1 (chromosome 4) and Gv-1 loci are linked at a distance of 19 units from one another. New data from other crosses show that this association of Gpd-1 (glucose-6-phosphate dehydrogenase 1) and GIX phenotypes also constitutes quasi-linkage, evidently due to heterozygosity at the Fv-1 locus. An important theoretical consequence of quasi-linkage in general is that it should enhance the heritability of particular constellations of unlinked genes, and so influence population structure. Our new data are discussed from the viewpoint that MuLV genomes are apparently concerned in quasi-linkage, and therefore by the same arguments may influence the genetic structure of populations. This in turn may strengthen the view that integrated MuLV genomes are not simply intruded into a self-sufficient cellular genome, but are themselves elements of the cellular genome with primary functions, perhaps in reproduction or embryogenesis.