THE ACCURACY OF MARKER-ASSISTED SELECTION FOR QUANTITATIVE TRAITS WITHIN POPULATIONS IN LINKAGE EQUILIBRIUM

Using the concept of conditional coancestry, given observed markers, a n explicit expression of the accuracy of marker-based selection is der ived in situations of linkage equilibrium between markers and quantita tive trait loci (QTL), for the general case of full-sib families neste d within half-sib families. Such a selection scheme is rather inaccura te for moderate values of family sizes and QTL variance, and the accur acies predicted for linkage disequilibrium can never be reached. The r esult is used to predict the accuracy of marker-assisted combined sele ction (MACS) and is shown to agree with previous MACS results obtained by simulation of a best linear unbiased prediction animal model. Low gains in accuracy are generally to be expected compared to standard co mbined selection. The maximum gain, assuming infinite family size and all QTLs marked, is about 50%.