Simulation of quantitative characters by genes with biochemically definable action. III. The components of genetic effects in the inheritance of anthocyanins in Matthiola incana R. Br.

In a self-pollinated plant species, Matthiola incana R. Br., six groups of isogenic lines were developed which were ideally suited for investigating the properties of individual genes controlling a quantitative character. Each group consisted of four homozygous parents for two alleles at each of the two loci in a common genetic background. A complete 4 × 4 diallel cross was obtained in each group. Because of the identical genetic background each diallel set could be considered as a genetic system of two loci. The biochemical functions of the alleles at each locus modifying the structure of the anthocyanin molecule were known. The phenotypes of the nine possible genotypes were qualitatively distinguishable by their flower colour differences. A quantitative measure of the phenotypic value associated with a genotype is the concentration of anthocyanins in flower tissues. In these simplified genetic systems, the nine phenotypic values could be expressed in terms of nine biometrical quantities, eight of which are attributable to the genetic effects of the alleles at the two loci under consideration. An unique solution of the set of nine equations in nine unknowns provided direct estimates of the parameters specifying additive, dominance and epistatic effects. Thus the effects of individual genes in a well-defined genetic background could be estimated by the use of a simple additive genetic model. An extension of the model provided estimates of the genetic parameters in different years and genetic backgrounds.Dominance was found to be the most important type of gene action in the inheritance of anthocyanin content in the flower tissues of M. incana. There was considerable epistasis, but the effect was very unstable over years and genetic backgrounds. The relative magnitude of additive effect was most stable. Heterosis was observed and was found to be largely due to dominance and additive × dominance interactions.