Genetic arrays and barcodes for chemical genomics. (a) In a genetic array, constructed mutants are maintained separately and are stamped onto no-drug or drug-containing petri dishes for time-dependent photographic analysis. (b) In a barcoding experiment, mutants are pooled and grown together with and without drugs. Growth of each of the mutants is assessed by hybridization of amplified barcodes to a microarray (the barcodes are labeled with Cy3 or Cy5 fluorescent dyes). Because particular mutant strains may have drug-free growth defects and/or lower barcode microarray signal efficiency, drug sensitivity or resistance can only be scored for a particular strain in comparison to its behavior without a drug.