Variance components of fitness under the stabilizing selection scheme of Wright (1935) for metric characters are calculated, extending his original analysis to the case with any number of alleles and multiple characters assuming additivity of gene effects. They are calculated in terms of the moments of the effects of alleles at individual loci for the metric characters. From these formulas, the variance components of fitness are evaluated at the mutation–selection equilibria predicted by the ‘Gaussian’ approximation (Lande, 1976), which is applicable if the per locus mutation rate is high, and the ‘House of Cards’ approximation (Turelli, 1984), which is applicable if the per locus mutation rate is low. It is found that the additive variance of fitness is small compared to non-additive variance in the ‘Gaussian’ case, whereas the additive variance is larger than non-additive variance in the ‘House of Cards’ case if the number of loci per character and the number of characters affected by each locus are not too large. With the assumption that a significant portion of fitness is due to this type of stabilizing selection, it is suggested that the real parameters are in the range where the ‘House of Cards’ approximation is applicable, since available data on variance components of fitness components in Drosophila show that the additive variance is far larger than the non-additive variance. It is noted that the present method does not discriminate the two approximations if the average values of the metric characters deviate from the optimum values. Other limitations of the present method are also discussed.
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