Inheritance of Multiple Traits

Abstract

Abstract The G-matrix provides a useful way to model inheritance when multiple traits are affected by many genes and genetically coupled. The G-matrix is an m trait × m trait table with genetic variances on its main diagonal and genetic covariances elsewhere. The genetic covariance between two traits summarizes genetic connections arising from linkage disequilibrium and/or pleiotropy. Studies of multiple trait inheritance often reveal appreciable genetic correlations between traits, especially when those traits are size-related. The M-matrix summarizes the patterns of mutational effects on multiple traits. Just as covariances among relatives are the foundation for estimation of the G-matrix, the accumulation of mutations in inbred lines is the foundation for estimation of the M-matrix. Studies of G- and M-matrices suggest that these matrices have almost as many dimensions of variation as the number of characters included in the study. Consequently, these matrices are unlikely to constrain the course of evolution on long evolutionary timescales. The entire G-matrix, as well as its constituent genetic variances and covariances, can be visualized as achieving a stable balance between opposing forces. This stable equilibrium represents a compromise between alternative structures imposed by the processes of selection, mutation, recombination, and migration.