It is widely held that each gene typically affects many characters, and that each character is affected by many genes. Moreover, strong stabilizing selection cannot act on an indefinitely large number of independent traits. This makes it likely that heritable variation in any one trait is maintained as a side effect of polymorphisms which have nothing to do with selection on that trait. This paper examines the idea that variation is maintained as the pleiotropic side effect of either deleterious mutation, or balancing selection. If mutation is responsible, it must produce alleles which are only mildly deleterious (s & 10(-3)), but nevertheless have significant effects on the trait. Balancing selection can readily maintain high heritabilities; however, selection must be spread over many weakly selected polymorphisms if large responses to artificial selection are to be possible. In both classes of pleiotropic model, extreme phenotypes are less fit, giving the appearance of stabilizing selection on the trait. However, it is shown that this effect is weak (of the same order as the selection on each gene): the strong stabilizing selection which is often observed is likely to be caused by correlations with a limited number of directly selected traits. Possible experiments for distinguishing the alternatives are discussed.
Thanks to JERRY COYNE, BILL HILL, LINDA PARTRIDGE, MICHAEL TURELLI, and two anonymous reviewers for their critical comments. This work was supported by grants from the National Science Foundation (BSR-8866548) the Science and Engineering Research Council (GR/E/08507), and by the Institute of Theoretical Dynamics, University of California, Davis.
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Barton NH. Pleiotropic models of quantitative variation. Genetics. 1990;124(3):773-782. doi:10.1093/genetics/124.3.773
Barton, N. H. (1990). Pleiotropic models of quantitative variation. Genetics. Genetics Society of America. https://doi.org/10.1093/genetics/124.3.773
Barton, Nicholas H. “Pleiotropic Models of Quantitative Variation.” Genetics. Genetics Society of America, 1990. https://doi.org/10.1093/genetics/124.3.773 .
N. H. Barton, “Pleiotropic models of quantitative variation,” Genetics, vol. 124, no. 3. Genetics Society of America, pp. 773–782, 1990.
Barton NH. 1990. Pleiotropic models of quantitative variation. Genetics. 124(3), 773–782.
Barton, Nicholas H. “Pleiotropic Models of Quantitative Variation.” Genetics, vol. 124, no. 3, Genetics Society of America, 1990, pp. 773–82, doi:10.1093/genetics/124.3.773 .
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