Refer to the metabolic pathway illustrated above. If A, B, and C are all required for growth, a strain that is mutant for the gene-encoding enzyme A would be able to grow on medium supplemented with .A) nutrient A onlyB) nutrient B onlyC) nutrient C onlyD) nutrients A and C

A) nutrient A only

Explanation:

In this case, enzyme A is required for the digestion of nutrient A, thereby evidencing that the mutation affects the enzymatic pathway and the mutant strain only can grow by supplementation with this nutrient. In molecular biology, mutant strains are useful to study enzymatic functions (for instance, the role of enzyme A in nutrient assimilation), as well as to examine downstream signaling pathways.

In experimental design, spontaneous mutations are induced to study their effects on the phenotype. Subsequently, reverse mutations may also be induced to reverse the forward mutation, thus restoring the original wild-type phenotype.