A pool of five barcoded yeast mutants, each deleted for a different gene (genes A to E), has been grown under three different conditions (1 to 3). After the growth phase was completed, genomic DNA was isolated from the entire pool and the relative amount of each mutant was determined by quantifying the amount of DNA containing each barcode. The results are presented in the following graph. Which gene (A to E) is essential under condition 1 but not under conditions 2 or 3?