Selective effects of H2z in F1 × NZB backcross mice vs. H2d in F1 × NZW backcross mice. The data are presented as linkage values (MLS) for H2d/z vs. H2d/d in F1 × NZB backcross mice and for H2d/z vs. H2z/z in F1 × NZW backcross mice. MLS > 1.4, P < 0.01; MLS > 2.35, P < 1 × 10−3; MLS > 3.3, P <1 × 10−4; MLS > 4.23, P < 1 × 10−5. Data are derived from 148 F1 × NZB mice followed for nephritis, 131 F1 × NZB mice studied serologically, 108 F1 × NZW mice followed for nephritis, and 92 F1 × NZW mice studied serologically.