R/qtl analysis of N2 progeny shows 3 QTLs that modify VWF plasma levels. Interval mapping was performed on natural log-transformed mean VWF levels. (A) LOD scores with adjustment for sex show 3 QTLs on chromosomes 6, 10, and 5 (Mvwf5, Mvwf6, and Mvwf7, respectively). No additional loci were identified by analysis for additive (B) or epistatic (C) effects upon adjustment for Mvwf5. Solid, dashed, and dotted lines indicate α = 0.25 (suggestive), 0.05 (significant), and 0.01 (highly significant) thresholds, respectively, obtained by permutation testing.