Posterior probability density pQ(x) for QTL presence. Data were simulated for 12 chromosomes with genome length G = 3600 cM, n = 1200 progeny, and 10 QTL with QTL heritabilities as shown. For each chromosome, marginal probabilities for models of size 0, 1, 2 QTL are p0, p1, p2, respectively. QTL locations are denoted with an asterisk. Likelihood ratios for interval mapping (– – –) and composite interval mapping (· · ·) are shown for comparison.