THE CONTRIBUTION OF QUANTITATIVE TRAIT LOCI AND NEUTRAL MARKER LOCI TO THE GENETIC VARIANCES AND COVARIANCES AMONG QUANTITATIVE TRAITS IN RANDOM MATING POPULATIONS

Using Cockerham's approach of orthogonal scales, we develop genetic mo dels for the effect of an arbitrary number of multiallelic quantitativ e trait loci (QTLs) or neutral marker loci (NMLs) upon any number of q uantitative traits. These models allow the unbiased estimation of the contributions of a set of marker loci to the additive and dominance va riances and covariances among traits in a random mating population. Th e method has been applied to an analysis of allozyme and quantitative data from the European oyster. The contribution of a set of marker loc i may either be real, it hen the markers are actually QTLs, or apparen t, when they are NMLs that are in linkage disequilibrium with hidden Q TLs. Our results Show that the additive and dominance variances contri buted by a set of NMLs are always minimum estimates of the correspondi ng variances contributed by the associated QTLs. In contrast, the appa rent contribution of the NMLs to the additive and dominance covariance s between two traits may be larger than, equal to or lower than the ac tual contributions of the QTLs. We also derive an expression for the e xpected variance explained by the correlation between a quantitative t rait and multilocus heterozygosity. This correlation explains only a p art of the genetic variance contributed by the markers, i.e., in gener al, a combination of additive and dominance variances and, thus, provi des only very limited information relative to the method supplied here .