Table 1 The results of the clustering tests on the different pairs of genes; each cell in the table contains the indices of the null hypotheses which were rejected (ranging from 1 to 3). Empty cell means that none of the null hypotheses were rejected, and hence the genes are similar. Due to symmetry, cells below the diagonal are not marked. Tests 1–3 compare the substitution count distribution through (1) Kruskal-Wallis, (2) negative-binomial model and (3) negative-binomial regression. The resulting clusters by our tests are (NDCO: ND1–6, CO1–3), (ATP: ATP6, ATP8) and CYB