Genetic fine-structure of theGA-1locus in the higher plantArabidopsis thaliana(L.) Heynh

SUMMARY Non-germinating gibberellin (GA) responsive mutants are a powerful tool to study genetic fine structure in higher plants. Nine alleles (EMS-and fast neutron-induced) of thega-1locus ofArabidopsis thalianawere tested in a complete half-diallel. No wild type ‘recombinants’ were found in the selfed progeny of 9 homoallelic combinations (in total 3 × 105plants); in the progenies from the 36 selfed hetero allelics the wild type frequency ranged from zero to 6·6 × 10−4. These frequencies allowed the construction of an internally consistent map for five different sites representing eight alleles. The ninth allele covered three sites and thus behaved like an intragenic deletion. The estimate of the total genetic length of thega-1locus was 0·07 cM. The order of the sites was also clearly reflected by the association with proximal outside markers. On the assumption that wild type gametes predominantly arise from reciprocal events, it was shown that a cross-over within thega-1locus leads to positive interference in the adjacent region. The results are discussed with respect to the mutagen used, the frequencies found in other plant and Drosophila genes, and the possible occurrence of gene conversion.