Before revision:  ii) how the conservationof genes , measured both by the evolutionary retention index (ERI) and by evolutionary pressure (as represented by the ratio K_a/K_s  ) is related to the the degree of the corresponding protein in the PPI network ;
After revision:  ii) how the conservationof genes , measured both by the evolutionary retention index (ERI) and by evolutionary pressure (as represented by the ratio K_a/K_s ) is related to the the connectivity of the corresponding protein in the PPI network ;