Long-term selection by using QTL-information

A quantitative trait is assumed to be genetically affected by a polygenic effect and a major effect of a single dialellic locus. Such an identified gene is denoted as quantitative trait locus (QTL). A population characterized by infinite population size, heritability equal to 0.4, ratio of QTL-variance and total genetic variance equal to 20% and complete dominance at the QTL was considered. The objective of the study was to investigate the genetic changes in the population over 20 generations of selection in five different environmental situations. The scenarios differed in the environmental variation of the three QTL-genotypes and also in heritability level after the favourable allel being fixed. To selection over generations indexes were constructed including the breeding value for the known QTL, the genotypic value of the QTL and the estimated polygenic breeding value. Beside of selection on phenotype and standard-indexes a sub-optimal index contracted the environmental variances at the QTL was considered in the model. If the favourable QTL-genotype is highly affected by the environment than it can be of advantage to select against the favourable allel. Deterministic calculations confirmed greater long-term response for sub-optimal strategies over standard indexes and phenotypic selection, not only for the up-selection but for the down-selection as well. The results from the deterministic approach showed good agreements with the results obtained by stochastic simulation.