A General Procedure for Predicting Rates of Inbreeding in Populations Undergoing Mass Selection

Predictions of rates of inbreeding (ΔF), based on the concept of long-term genetic contributions assuming the infinitesimal model, are developed for populations with discrete or overlapping generations undergoing mass selection. Phenotypes of individuals are assumed to be recorded prior to reproductive age and to remain constant over time. The prediction method accounts for inheritance of selective advantage both within and between age classes and for changing selection intensities with age. Terms corresponding to previous methods that assume constant selection intensity with age are identified. Predictions are accurate (relative errors ≤8%), except for cases with extreme selection intensities in females in combination with high heritability. With overlapping generations ΔF reaches a maximum when parents are equally distributed over age classes, which is mainly due to selection of the same individuals in consecutive years. ΔF/year decreases much more slowly compared to ΔF/generation as the number of younger individuals increases, whereas the decrease is more similar as the number of older individuals increases. The minimum ΔF (per year or per generation) is obtained when most parents were in the later age classes, which is mainly due to an increased number of parents per generation. With overlapping generations, the relationship between heritability and ΔF is dependent on the age structure of the population.