EFFECT OF INCLUDING MAJOR GENE INFORMATION IN MASS SELECTION - A STOCHASTIC SIMULATION IN A SMALL POPULATION

A quantitative trait under the control of a major gene plus a finite n umber of genes with small effects was described using a stochastic mod el where number, size and linkage between QTL may vary. Selection sche mes defined by the selection criteria (individual phenotype, major gen otype and combination of both sources of information), the population size and the selection intensities in male and female paths were consi dered. Different genetic hypotheses were studied concerning the major gene effect, the number of small quantitative loci and the linkage bet ween genes. The ranking of the selection schemes over 30 generations w as performed with the following criteria: time taken for the fixation of the favourable A allele at the major locus and differences between the cumulated discounted gains obtained with each scheme. The interact ions between the major gene and the flanking QTLs were also studied. T he main result was that the inclusion of major gene information in sel ection schemes was mostly efficient in the medium and long term when t he gene was rare and recessive and in the medium term when it was rare and additive, essentially due to a rapid fixation of the favourable A allele and to a limited risk of losing it by genetic drift for a rare recessive gene.