It has been shown previously that, even in the absence of linkage, selection can cause an appreciable change in the genetic variance of a metric character due to disequilibrium; this change is temporary and is rapidly reversed when selection ceases. This result is here extended to allow for the effect of linkage, and it is shown that the change in the variance is effectively determined by the harmonic mean of the recombination fractions. The validity of the approximate general formula derived here has been checked by comparison with exact results obtained from models with five or six loci. In order to determine the likely value of the harmonic mean recombination fraction, a simple model was constructed in which it was assumed that loci are distributed at random along the chromosome maps. Results of computer simulations of this model are reported for different chromosome numbers and numbers of loci.

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