QUANTITATIVE GENETICS IN PLANTS - THE EFFECT OF THE BREEDING SYSTEM ON GENETIC-VARIABILITY

The expected effects of breeding system on quantitative genetic variat ion under various models for the maintenance of such variation are exa mined, with particular emphasis on the contrast between randomly matin g and highly self-fertilizing populations. Estimates of quantitative g enetic parameters from plant populations are reviewed. There is some e vidence for reduced within-population genetic variance in highly inbre eding populations, compared with outbreeders, but more empirical work appears necessary. Although the estimate of the magnitude of the effec t of breeding system is subject to considerable error, the reduction i n genetic variance in inbreeding populations appears greater than expe cted if the variation were maintained by overdominance, or if it were due to neutral mutations. It is more consistent with models involving mutation-selection balance, although a rather larger reduction in gene tic variance is estimated than is expected theoretically. We discuss s ome possible reasons for the lower level of genetic variance in selfer s than is predicted by such models.