Mutant screen

Deduce the pathway order from auxotroph growth

This puzzle is based on the classic Beadle and Tatum Neurospora mutant auxotroph experiments that led to the "one gene, one enzyme" hypothesis. Each mutant class is blocked at a different step in a metabolic pathway. A blocked mutant can only grow if you supply a downstream intermediate that bypasses the block.

Auxotroph solving tips I need help: show first step (-1 guess)

How to solve the auxotroph puzzle

Your goal is to determine the order of metabolites in a biosynthetic pathway using mutant growth data.

1. Each mutant class has a block at a different step in the pathway.
2. A mutant grows (+) only when supplemented with an intermediate downstream of its block.
3. A mutant does not grow (–) when given an intermediate upstream of its block.
4. Count the plus signs: the class with only one + is blocked latest (just before the final product); the class with all + is blocked earliest.
5. Order the metabolites from first to last in the pathway. The correct order spells a five-letter English word.