Ratio of the observed and expected medaka orthologs of human genes in human chromosomes. The distribution pattern of 818 human orthologs is similar to that of 45,910 human genes in each human chromosome except Hsa 12, 13, 17, and 18. This indicates that the mapped medaka genes orthologous to human have been selected rather randomly. Mapped human orthologs are more frequently observed in Hsa 12 and 17 and less frequently observed in Hsa 13 and 18, indicating the mammalian-specific expansion of gene number in Hsa 13 and 18 and reduction of gene number in Hsa 12 and 17.