Comparative analysis of association and dispersion crosses to detect linkage and epistatic components of variation

Abstract

In theory, a matched pair of crosses in which the pure breeding parents display association and dispersion for the same alleles at the same loci provides sensitive tests for the presence of complex sources of variation. Thus comparison of the genetical component of variation within the F2 and first backcross families of such a pair of crosses can detect and distinguish between non-allelic interaction, a linkage disequilibrium of non-interacting genes and a linkage disequilibrium of interacting genes. These theoretical expectations are confirmed by analyses of two sets of matched association and dispersion pairs of crosses involving pure breeding varieties 1 and 5, and 2 and 12 of Nicotiana rustica and pure breeding selections for final height extracted from crosses between them by single seed descent. Furthermore, these analyses show that comparison of the genetical components of the variation within F2, B1 and B2 families of matched association and dispersion crosses are more sensitive to non-allelic interaction and linkage disequilibrium than much larger and more complex experiments based on a single cross and analysed by conventional model fitting procedures.