The effect of selection in sublines and crossing on genetic response and inbreeding

More intense selection in a line gives greater genetic change but also gives a higher rate of inbreeding. Here, continuous selection in one line vs continuous selection in two or more sublines (for the same breeding objective and with the same total number of individuals tested) and crossing the sublines to reduce inbreeding, is studied by stochastic simulation using an infinitesimal model. On crossing, the inbreeding level in the cross, though zero, becomes equivalent to 1/n times that in the sublines, where n is the number of lines in the cross. In general, selecting in sublines and crossing gave less genetic response at the same level of inbreeding than selection in a single line. Use of the best subline generally gave less response than the whole line. It is concluded that selection response at the same level of inbreeding is greatest when all the test facilities and selection are concentrated in a single selection line.