Using the NDB database, we calculated geometrical parameters that were needed to reproduce crystal structures of short DNA fragments in a phosphorus atom representation. The geometrical parameters were included in a software generating tertiary structures of, for example, the Escherichia coli and human chromosome 21 molecules of DNA whose complete nucleotide sequences are deposited in the EMBL and related databases. Both molecules were found to be heavily folded and composed of domains. A more elaborate version of the present approach will make analysis and comparison possible of tertiary structures of genomic DNA molecules of various chromosomes to identify the chromosome evolutionary and functional relationships.