DIRECT EVIDENCE FOR MODELS OF HETEROSIS PROVIDED BY MUTANTS OF ARABIDOPSIS BLOCKED IN THIAMINE PATHWAY

Auxotrophic mutants genetically blocked at different steps of the thiamine pathway dramatically demonstrate the biochemical mechanism of hybrid vigor due to simple and perfect dominance at two unlinked loci. Heteroallelic hybrids of mutants requiring the pyrimidine moiety of thiamine display allelic complementation and thus furnish clear biochemical and genetic evidence for the superdominance hypothesis. Hybrids of low- and high-temperature-requiring leaky mutants demonstrate that heterozygosity at a single gene locus may confer developmental homeostasis on the heteroallelic combinations superior to that of the homoallelic parents. The results of this study on the autogamous plant, Arabidopsis, and of recent reports on the outbreeding species, Drosophila, render untenable the generalization that high versus low temperature dependent heterosis is determined by the breeding system. © 1969 Springer-Verlag.