A technique for selection of DNA sequences common to two DNA populations. Of the two populations, the one of lowest complexity (or one made least complex by the creation of representations) is used in excess over the other population; it is cleaved by a restriction endonuclease and the fragments are ligated to linker oligonucleotides that will serve as primers, one of which is biotinylated; the other DNA population is cleaved by the same endonuclease. The two populations are mixed, denatured and annealed, and biotinylated fragments (i.e. including those from the second population that are also represented in the first) are isolated on a solid support, based on the presence of biotin. (The non-shared fragments from the second source are washed away.) The recovered fragments are then exposed to 'capture' oligonucleotides that are complementary to the linker oligonucleotides and will therefore be placed adjacent to the strands that originated in the second population; these strands are then ligated to the capture oligonucleotides. PCR using primers complementary to the capture oligonucleotides amplifies these fragments, which can be released from the primers by the endonuclease.