Single- and multiple-trait mapping analysis of linked quantitative trait loci: Some asymptotic analytical approximations

Estimating the resolution power of mapping analysis of linked quantitative trait loci (QTL) remains a difficult problem, which has been previously add ressed mainly by Monte Carlo simulations. The analytical method of evaluati on of the expected LOD developed in this article spreads the "deterministic sampling" approach for the case of two linked QTL for single- and two-trai t analysis. Several complicated questions are addressed through this evalua tion: the dependence of QTL detection power on the QTL effects, residual co rrelation between the traits, and the effect of epistatic interaction betwe en the QTL for one or both traits on expected LOD (ELOD), etc. Although thi s method gives only an asymptotic estimation of ELOD, it allows one to get all approximate assessment of a broad spectrum of mapping situations. A goo d correspondence was found between the ELODs predicted by the model and LOD values averaged ol er Monte Carlo simulations.