GENETIC-STUDIES OF ASSORTATIVE MATING - A SIMULATION STUDY .3. ASSORTATIVE MATING IN SELECTED POPULATIONS

Effects of 25 generations of positive assortative mating, random matin g and negative assortative mating in simulated selected populations of various effective size (N-e = 40, 100, 200) were compared. The trait under consideration was controlled by either 100 or 2500 loci. Positiv e assortative mating produced the highest cumulative selection respons e (11.61-13.24 sigma(P)), followed by random mating (11.00-12.48 sigma (P)) and negative assortative mating (10.88-11.98 sigma(P)). The diffe rences between the various mating systems were highly significant (P < 0.001) after the second generation and depended on the covariance due to linkage disequilibrium (C-l) and varying rates of fixation of the favourable alleles, leading to different genic variance (V-a). Positiv e assortative mating first caused C-l to increase to maximum values eq ual to 10.8% of the base population genetic variance (V-A) when the tr ait was controlled by 100 loci and then to decline gradually. A faster rate of change in gene frequency caused V-a to decrease initially, bu t to return towards random mating levels later (after generations 13-1 7 when the trait was controlled by 100 loci), when fixation of the fav ourable alleles approached completion. Inbreeding coefficient and degr ee of homozygosity increased slightly under positive assortative matin g. Negative assortative mating had similar, but smaller, effects on C- l and V-a in the opposite direction of positive assortative mating.