An Experiment Is Performed with a Mutant Yeast Strain That

An experiment is performed with a mutant yeast strain that cannot survive without being given tryptophan. The yeast strain is transformed with a plasmid containing gene A or a plasmid containing gene B. Yeast cells transformed with gene B require supplementary tryptophan to survive, but yeast transformed with gene A can survive in the absence of tryptophan. Which of the following conclusions can be drawn from this experiment? Please select all that apply.

A) Gene A is needed for tryptophan synthesis
B) Gene B is needed for tryptophan synthesis
C) Tryptophan is essential for growth in this yeast species
D) Gene A is not needed for tryptophan synthesis
E) Gene B is not needed for tryptophan synthesis