In their first round of screening, Beadle and Tatum plated spores on minimal medium. The purpose of this screen was to .
1. eliminate all nonmutant Neurospora from the population
2. determine which of the mutants generated were auxotrophic for thiamine
3. determine whether any auxotrophic mutants had been generated
4. identify which mutants were deficient in vitamin synthesis pathways and which were deficient in amino acid synthesis pathways