Genetic analysis and genetic modifiers A mutagenesis screen was carried in Arabidopsis thaliana to identify plants with reduced in leaf area. After an F1 Complementation Test, mutations in six different genes had been identified. Three separate experiments were carried out to investigate the interactions between these genes. In each experiment the average leaf area was calculated for wild-type plants, plant homozygous for each single mutant, and also the double mutants, which were homozygous for both mutations. For each experiment provide an explanation for the interaction between each pair of genes. Experiment 1 Compared to wild-type (AA; BB), plants that are homozygous recessive for mutations in gene a (aa; BB) show a 52% reduction in leaf area, and plants homozygous for gene b (AA; bb) a 48% reduction in leaf area. Plants that are homozygous for mutations in gene a and b (aa; bb) show the same leaf area as wild-type leaves. leaf area 100 75 50 25 0 Wild-type aa; BB AA; bb aa; bb AA; BB aa; BB AA; bb aa; bb Experiment 2 Plants that are homozygous mutants for a mutant in the c gene (cc; DD) show a 38% reduction in leaf area, and plants homozygous for a mutation in gene d (CC; dd) have a 44% reduction in leaf area. The cc; dd double has very narrow leaves and shows a 88% in leaf area. leaf area 100 75 50 25 0 Wild-type cc; DD CC; dd cc; dd CC; DD cc; DD CC; dd cc; dd Experiment 3 Plants that are homozygous for mutations in the e gene (ee; FF) show a ~35% reduction in leaf area, and plants homozygous for a mutation in gene f (EE; ff) have ~35% reduction in leaf area. The ee, ff double also has a ~35% reduction in leaf area. leaf area 100 75 50 25 0 Wild-type ee; FF EE; ff ee, ff EE; FF ee; FF EE; ff ee; ff
Answers: Experiment 1: The double mutant is less severe than either of the single mutants aa and bb. Both a and b are acting as suppressors. The A and B genes are likely to affect leaf area through different or separate pathways. There is some evidenced they may have opposite or possibly antagonistic interactions because the double mutant is a similar size to wild-type. You might want to think about the segregating ratios you might see in F2 cross. If you consider the data available for area you would expect to see an ratio of 10:3:3. But if you consider shape and area then the ratio you could determine is is 9:3:3:1 because the shape leaves in the double mutant differ from wild type. This is a reasonable conclusion and reveals more about the function of the genes that have been identified by mutagenesis. Both A and B have a role in determining the size of wild type leaves, but the phenotype of b also indicates that this gene determines the shape of wild type leaves. The