When a tandem cluster of membrane proteins contains paralogs, the cluster size and the numbers of transmembrane segments in paralogous membrane proteins may be used to assign functions. Here the likelihood of being a transporter (A or B in Fig. 2) rather than in another functional category (C in Fig. 2) is shown by the darkness in three levels, darker meaning more likely. The likelihood is defined by the relative frequency and the absolute number of transporters in Figure 2 (see text for details).