Predicted and observed fitness values of various gene deletion strains of S. cerevisiae (Sc) and S. pombe (Sp). (A–D) Predicted fitness values based on various hypotheses. (E,F) Observed fitness values. In all panels, one-to-one, two-to-one, and one-to-two orthologs between Sc and Sp are indicated by gene trees. A solid circle indicates the deleted gene(s) in the strain whose fitness is presented. The dashed line shows the corresponding wild-type fitness. (A) Expected fitness relationships when deleting one-to-one orthologs in Sc and Sp have similar fitness effects (left) and when they have different effects (right). (B) Expected fitness relationships when less important genes tend to duplicate (left) and when gene importance does not impact the probability of gene duplication (right). (C) The expected fitness relationship when gene duplication facilitates adaptation (left) and when it does not promote adaptation (right). (D) The expected fitness relationship under the theoretically maximal fitness gain after gene duplication (left) and that under a smaller fitness gain (right). (E) Observed mean fitness values of various gene deletion strains. The six columns contain 1620, 135, 156, 156, 1620, and 253 genes or gene pairs (left to right). There are fewer gene pairs in bar III compared with bar VI because the fitness values of some double deletion strains are unavailable. Error bars show one standard error and P-values are from Mann-Whitney U tests. (F) Quantile–quantile plot of fitness gains in Sc, relative to Sp. The x-axis shows the quantiles of the fitness difference between Sp and Sc strains lacking one-to-one orthologs, whereas the y-axis shows the corresponding quantiles of the fitness difference between Sp and Sc strains lacking two-to-one orthologs. Each dot represents a two-to-one orthologous trio (y-axis) and the corresponding one-to-one orthologous pair (x-axis) that has the closest quantile to the two-to-one trio. Red dots are duplicates with fitness gains (DWFG), whereas blue dots are duplicates without fitness gains (DWOFG).
