Answer:
Arginine
Explanation:
The biochemical pathway for synthesis of arginine from its precursor includes the formation of ornithine from precursor. Ornithine serves as precursor for formation of citrulline which is then converted into arginine.
The "arg-3" mutants of Beadle and Tatum experiment were defective in the gene that code for the enzyme required to convert citrulline into arginine. These mutants could grow only when arginine was supplemented in the medium.
