Identification of duplicate and singleton genes

for each media condition as the extent of survival and reproduction (fitness) of the deletion strain relative to the pool of all strains grown and measured collectively. Fitness values (f) of 1.0 indicate no difference between a single strain and the pool average for that condition; f , 1.0 indicates that the strain is less fit, and f . 1.0 indicates that the strain is more fit than the pool average. In addition, we added to our analysis 1,060 ORFs that each had a lethal effect when deleted and assayed in YPD; we used only lethal deletions that could be inferred as lethal from both of the two studies conducted. We divided all genes into four groups according to the f value as follows: (1) if f . 0.95 for all five media conditions, the deletion has a weak or no fitness effect in all conditions; (2) if 0.8 # fmin , 0.95, where fmin is the smallest f value for all five growth conditions, the deletion has a moderate effect; (3) if 0 , f min , 0.8, the deletion has a strong effect; and (4) if the deletion is lethal, we set f 1⁄4 0.