The study of biochemical mutants in organisms such as Neurospora has demonstrated that some pathways are branched. The data shown in the following table illustrate the branched nature of the pathway resulting in the synthesis of thiamine: Growth Supplement _ Mutation Minimal Medium Pyrimidine Thiazole Thiamine thi-1 − − + + thi-2 − + − + thi-3 − − − + Why don't the data support a linear pathway? Can you postulate a pathway for the synthesis of thiamine in Neurospora?