¹Department of Forest Genetics and Plant Physiology, UPSC, SLU, Umeå, Sweden

Correspondence: Dr P Waldmann, Department of Forest Genetics and Plant Physiology, UPSC, SLU, Umeå SE-901 83, Sweden. E-mail: Patrik.Waldmann@genfys.slu.se

Received 3 March 2006; Revised 7 December 2006; Accepted 19 January 2007; Published online 28 February 2007.

Abstract

Additive genetic variance might usually be expected to decrease in a finite population because of genetic drift. However, both theoretical and empirical studies have shown that the additive genetic variance of a population could, in some cases, actually increase owing to the action of genetic drift in presence of non-additive effects. We used Monte–Carlo simulations to address a less-well-studied issue: the effects of directional truncation selection on a trait affected by non-additive genetic variation. We investigated the effects on genetic variance and the response to selection. We compared two different genetic models, representing various numbers of loci. We found that the additive genetic variance could also increase in the case of truncation selection, when dominance and epistasis was present. Additive-by-additive epistatic effects generally gave a higher increase in additive variance compared to dominance. However, the magnitude of the increase differed depending on the particular model and on the number of loci.