The frequency of membrane proteins that are paralogous within a tandem cluster, where each membrane protein is classified according to the number of transmembrane segments and the size of the cluster to which it belongs. The criterion for a paralog is the same as in Figure 1. The frequency is counted separately for three functional groups: (A) ABC transporters; (B) transporters other than ABC transporters; and (C) membrane proteins of other functions. In total, 256 clusters (13.0%) contained such pairs of paralogous membrane proteins, and among them, 98 (38.3%) were those of ABC transporters, 37 (14.5%) were those of other transporters, 63 (24.6%) were those of the other functions, and 58 (22.7%) were those of hypothetical functions (not shown).
