Setting Cov(Yi, Yj) = 2 ϕij for opposite sex individuals assumes that the same genes influence phenotypes for males and females. We also evaluated a model in which the covariance for individuals of opposite sexes was Cov(Yi, Yj) = 2 ϕij ρsex , but we found no cases where this model (with −1 < ρsex < 1) resulted in a significant improvement in the likelihood. Thus, our data provide no evidence that different genes contribute to genetic variation in males and females, but rather that the same genes make different contributions in each sex.
