EFFECTS OF A SINGLE QTL ON THE ASYMMETRY OF THE DISTRIBUTION OF A TRAIT

In this paper the mixed polygenic and single locus model of inheritanc e is investigated, whereby the genetic expression of the quantitative trait is described by one bi-allelic locus and an infinite number of l oci (excluding the single one). Strictly additive gene action of the p olygenes is assumed but dominance is allowed at the major locus (QTL). For such a model explicit formulas for the skewness and the kurtosis are derived as functions of the frequency of the favourable allele, th e heritability and the variances due to the major locus and to the pol ygenic effects. Using genetic parameters estimated with data from an e xperiment of laying hens, the distribution of the total genetic varian ce is investigated hypothetically, such that the observed degree of as ymmetry is obtained. QTL's explaining 40% of the total genetic varianc e and a frequency about 0.8 of the favourable allele have to be assume d to explain the observed asymmetrical distributions of the traits gen etically.