Results Quite a few homologous pairs of proteins exist among all of 22 autosomes and two sex-chromosomes. Two such examples are shown in Figure 2 and Figure 3 . Interestingly, many homologous genes are focused on certain chromosomal bands. Such regions could be the position where extensive chromosomal regions have duplicated. To detect duplicated chromosomal regions between chromosomes, we looked for pairs of chromosomal bands on which three or more homologous genes exist.
Some regions have more than one duplicated regions.
Furthermore, four chromosomal regions, 10q24, 17q21, 19q13, and 22q13, seem to be homologous to each other. Figure 4 shows the distribution of the number of homologous genes on different chromosomes for all genes. Genes that have extremely large number of homologous genes seem to have multiple domains. We are constructing a database of duplicated human chromosomal regions, which is now partially open to the public via World Wide Web. Discussion Most of the duplicated chromosomal regions discovered in this study might be the result of regional, chromosomal, or genomic duplications in the past.