Question

Several haploid mutants are isolated, all of which require compound E for growth. The compounds (A to D) in the biosynthetic pathway to E are known, but their order is not known. Each compound is tested for its ability to support the growth of each mutant (1 to 6). In the following table a plus sign indicates growth and a minus sign indicates no growth. For each mutant 1-6, select the step of the pathway where it is defective. Choose the most specific correct answer.

I know the order of pathway CABDE, but I'm confused how to select the mutant. Please provide thorough explanation.

Mutant	Compound Tested	Compound Tested	Compound Tested	Compound Tested	Compound Tested
	A	B	C	D	E
1	+	+	-	+	+
2	-	-	-	-	+
3	-	+	-	+	+
4	+	+	-	+	+
5	-	-	-	+	+
6	-	+	-	+	+

Answer 1

One can deduce where in the pathway the mutant is affected by looking at its growth pattern. No growth indicates abrogation of that particular gene function. If there is no growth in many compounds suggesting that the one which is downstream in the metabolic pathway is the one which is affected.

Hence

Mutant 1- formation of c

Mutant 2- formation of D

Mutant 3- formation of A

Mutant4- fomation of C

Mutant 5-. Formation of B

Mutant 6- formation of A