Glucosinolates are compounds produced by some species of plants and toxic to many insects. These compounds therefore provide a defense against those insects. Methylthioalkylmalate synthase (MAM) is an enzyme involved in the synthesis of glucosinolates.

a) Explain how you could you use DNA sequence data to test whether this enzyme has evolved in response to selection that favored new alleles at the locus that encodes MAM (i.e. positive selection) – be sure to explain what data you would need to conduct the analysis.

b) What would you expect to find if the MAM locus has evolved under strong purifying selection?