Ancestral median for human, mouse, and cat genomes found by MGR-MC. We used the gene order of 114 markers spread over the chromosomes in all three species. The numbers above the chromosomes correspond to these 114 markers, and the numbering is such that the human genome corresponds to the identity permutation broken into 20 pieces. The names below the chromosomes correspond to the name of the markers. We attribute a color to each human chromosome. The colorof any marker (in any genome) indicates the human chromosome on which the homolog of this marker lies. Each marker segment is traversed by a diagonal line. These diagonal lines are such that the human chromosomes are traversed from top left to bottom right and are designed to provide visual help to identify where rearrangements occurred. For example, for chromosome X, the gene order of the ancestor coincides with the cat gene order and only differs by one segment consisting of genes 108 and 109 (break in the diagonal line) from the human gene order. The mouse X chromosome is broken into 7 segments compared to the ancestor (shown by seven broken segments of the diagonal line).