where β1 and β2 are the regression coefficients of the additive and dominant parameters, respectively. The LOD score represents the difference in the log10 of the likelihood of the above two equations, where the individual model likelihoods are maximized with respect to the model parameters, given the marker genotype and phenotype data. If a trait y differs on average between the two sexes but the QTL has the same effect in both males and females, we can model this interaction by including sex as an additive covariate in the above models, resulting in the new model