Beadle and Tatum developed a method for isolating auxotrophic mutants in Neurospora

15.3 Beadle and Tatum established that each step in a pathway is controlled by a different enzyme. This biochemical pathway leads to the synthesis of arginine in Neurospora. Steps in the pathway are catalyzed by enzymes affected by mutants.

They first isolated a series of auxotrophic mutants whose growth required arginine. They then tested these mutants for their ability to grow on minimal medium supplemented with three compounds: ornithine, citrulline, and argi-nine. From the results, they were able to place the mutants into three groups (Table 15.1) based on which of the substances allowed growth. Group I mutants grew on minimal medium supplemented with ornithine, citrulline, or arginine. Group II mutants grew on minimal medium supplemented with either arginine or citrulline but did not grow on

Table 15.1 Growth of arginine auxotrophic mutants on minimal medium with various supplements

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