Use of comparative genomics to identify functionally related genes. This example of phylogenetic profiling shows gene comparisons for four organisms. P1 through P7 indicate proteins encoded by each species. The + or − indicates presence or absence of the protein. The technique does not require homologous proteins. Because proteins P3 and P6 always appear together in a genome (red shading), they may be functionally related. In particular, they may have a function that is found in species 1, 2, and 4, but not in species 3. Further testing would be needed to confirm this inference.