Fig. 2

Distribution of ortholog groups by the number of strains in which they are present. For each number of strains x, the number of genes y present in exactly x strains is given. The blue line corresponds to the approximation by a sum of three exponents y=e^−0.2x+8.4+e^−1.8x+11.6+e^{0.85x−100.1}; the red line corresponds to the approximation by a sum of two power functions y=21648.4x^−1.8+1182.8(128−x)^−1.2. Based on the Akaike information criterion (AIC), the approximation by the sum of three exponents recapitulates the U-shape slightly better