Abstract: Methods for global monitoring of gene expression and searching for useful genes that are targeted to organisms lacking sequence information are realized by providing low-cost and efficient DNA arrays. A genomic library constructed from randomly cleaved genomic DNA fragments is directly fixed on a substrate that allows the library to be individually recognized. In this way, global monitoring of gene expression can be carried out without being limited by the amount of gene sequence information. Further, plasmids that are detected by a constructed random genomic DNA array are fragmented into shorter DNAs, which are fixed on another substrate to construct a sub DNA array. With the use of this sub DNA array, gene expression is analyzed and useful genes are searched.